Grant Cohn: Examining state of the 49ers' roster

Before the 49ers decide what they need in the draft and free agency, they must take sober stock of what they have. They didn't do that last year.

They fell in love with themselves after a five-game winning streak to end the season which gave them the illusion they're better than they are. Then, they overvalued almost everyone who played during that streak, especially the players on defense.

Now, the defense has given up a grotesque 28 points per game this season, forcing just five turnovers — fewest in the NFL — and the 49ers' record is 2-10.

How many keepers do the 49ers really have on the current roster? Which players are the true building blocks of a serious team?

Let's count the fake franchise cornerstones, former cornerstones, potential cornerstones and legitimate cornerstones. And before we get started, yes, there's hope.

Group 1: Players formerly considered potential franchise cornerstones who are now expendable.

1. Defensive end Solomon Thomas. The worst defensive lineman on the 49ers. They probably would have cut Thomas by now had they not taken him with the third pick of the 2017 draft. He's a small, mediocre run-defending specialist who no longer plays during passing downs.

2. Wide receiver Marquise Goodwin. Seemed like a potential cornerstone during a six-week stretch late last season when he averaged 93.3 receiving yards per game. The 49ers rewarded Goodwin with a three-year, $19.25 million contract extension through 2021. But this season, Goodwin has caught just 17 passes and reverted to the injury-prone, unreliable receiver he was for four years with the Buffalo Bills.

3. Cornerback Ahkello Witherspoon. Intercepted two passes as a rookie last season, so the 49ers thought he was the next Richard Sherman. They handed Witherspoon a starting job for 2018, didn't make him compete for it. And so far, Witherspoon has intercepted no passes, given up six touchdown catches, committed nine penalties, thrown one notorious hissy fit in a game and gotten benched twice.

4. Free safety Adrian Colbert. Broke up a few throws and forced a couple fumbles last season, so the 49ers thought he was their free safety of the future. This season, Colbert forced no fumbles, broke up one pass, missed lots of tackles and lasted only seven games before a high-ankle sprain ended his season.

5. Strong safety Jaquiski Tartt. Injury prone since the 49ers drafted him in 2014. Made a few plays last season before breaking his arm, so the 49ers thought he was their strong safety of the future. They gave Tartt a two-year, $13 million extension and cut former Pro Bowler Eric Reid, who also plays strong safety. This season, Tartt remains injury prone — he has missed four games and won't play this Sunday. Meanwhile, Reid is a healthy starter for the Carolina Panthers.

6. Defensive back Jimmie Ward. The 49ers drafted Ward with a first-round pick in 2014. Since then, he has intercepted just two passes and been on the injured reserve list four times. He's on IR now.

7. Defensive end Arik Armstead. The 49ers drafted Armstead with a first-round pick in 2015, and he has just nine sacks in four seasons. When he gets close to the quarterback, he usually whiffs. He never improves.

8. Left guard Laken Tomlinson. A former first-round pick who was a bust for the Detroit Lions. They traded Tomlinson to the 49ers in 2017 for a fifth-round pick in 2019. Tomlinson struggled with the Niners last season, but they still gave him a three-year, $16.5 million extension on June 22. They thought they saw big talent in him. Last Sunday, Tomlinson gave up three sacks and committed two penalties. He's replaceable.

9. Center Weston Richburg. Played the first four seasons of his career with the New York Giants, who gave up on him this offseason. Let him go. The 49ers made him the second-highest-paid center in the NFL, and Kyle Shanahan compared him to Alex Mack, a five-time Pro Bowler. Richburg is a no-time Pro Bowler. Defensive linemen routinely knock him backward, and he snapped the ball over Nick Mullens' head last Sunday.

10. Guard Joshua Garnett. The 49ers drafted Garnett with a first-round pick in 2016. He has played just 29 snaps the past two seasons. Does he really want to play football?

11. Wide receiver Trent Taylor. Caught 43 passes as a rookie slot receiver in 2017. Had back surgery during the offseason, and seems to have lost the quickness that made him effective. Taylor has caught just 20 passes in 2018.

12. Wide receiver Kendrick Bourne. This season, Shanahan tried to make Bourne the primary red-zone target and eventual replacement for Pierre Garcon. But Bourne frequently lines up in the wrong spot or runs the wrong route. Quarterbacks can't trust him. He has just 29 catches for 317 yards this season.

13. Quarterback C.J. Beathard. The 49ers traded up to take Beathard in the third round of the 2017 draft, and Shanahan compared him to Kirk Cousins, the third-highest-paid quarterback in the league. But Beathard is no Cousins. Beathard has lost the 49ers' starting job twice, most recently to an undrafted quarterback. The 49ers probably couldn't trade Beathard if they wanted to.

Group 2: Players formerly considered franchise cornerstones who are getting old or declining.

1. Cornerback Richard Sherman. A 30-year-old future Hall-of-Fame corner who tore his Achilles last year and no longer has the quickness or recovery speed to play cornerback well. Opposing quarterbacks have picked on Sherman the past two weeks.

2. Left tackle Joe Staley. One of the greatest left tackles in the franchise history, but he's 34, and no longer can block an inside counter move consistently. Lacks the quickness. The 49ers need to find Staley's heir apparent. Too bad they traded Trent Brown, who now plays left tackle for the New England Patriots.

3. Wide receiver Pierre Garcon. The 49ers gave Garcon a five-year, $47.5 million contract in 2017. Nearly two years later, he has missed 12 games and caught just one touchdown pass. The 49ers almost certainly will release him this offseason.

Group 3: Players who have modest hopes to become franchise cornerstones, and maybe these hopes are justified.

1. Running back Jerick McKinnon. The 49ers gave McKinnon a four-year, $30 million contract, but he tore his ACL before the season. If he regains his speed and quickness — no guarantee — he could find success in Shanahan's offense. Most running backs do.

2. Running back Raheem Mostert. Has carried the ball only 41 times in his career, but averages 7.7 yards per carry. That's gargantuan. And Mostert is excellent on special teams. But he's on IR with a broken forearm. He needs to show he's durable.

3. Running back Jeff Wilson Jr. Has played just two NFL games, but gained 134 all-purpose yards last week against the Seattle Seahawks. Wilson is fast and powerful, which makes him unique to the 49ers. The other running backs are just fast.

4. Wide receiver Dante Pettis. Missed most of this season with a knee injury, but started the past two games, caught three touchdown passes and gained 206 receiving yards. Needs to stay healthy and play well for more than two games.

5. Defensive tackle Jullian Taylor. A rookie seventh-round pick, and the most violent, disruptive 49ers defensive lineman other than DeForest Buckner during the preseason. Taylor rarely plays during the regular season, though. Maybe he'll play more next season if the 49ers hire a new defensive coordinator.

6. Quarterback Nick Mullens. Through just four games, Mullens has established he's a quality backup quarterback and possibly even a future long-term starter. He had one of the greatest debuts by a quarterback in NFL history. And last week, he threw for 414 yards against the Seahawks in Seattle's CenturyLink Field, the loudest and most difficult place for a quarterback to play. The only other quarterbacks since 2010 to pass for more than 400 yards against the Seahawks in Seattle are Drew Brees, Ben Roethlisberger, Deshaun Watson and Philip Rivers. Four of the best quarterbacks in the league.

Group 4: Players who have reasonable hopes to become franchise cornerstones.

1. Running back Matt Breida. Replaced McKinnon as the starting running back just before the regular season began, then injured his hip Week 3 and his ankle Week 5. Still averages 5.6 yards per carry. Breida has played through pain and produced. He should remain the starting running back in 2019 even if McKinnon is healthy.

2. Linebacker Fred Warner. Talented, smart and a leader. One of the team's most professional players. The middle linebacker the 49ers hoped Reuben Foster would be but wasn't. Warner could become a Pro Bowler in the next couple of seasons. He's just a rookie.

3. Right tackle Mike McGlinchey. A solid right tackle who even played some right guard this season, but must move to left tackle before we consider him a cornerstone. McGlinchey may not pass block well enough to play left tackle. Run blocking is his strength.

Group 5: Players who could become definite franchise cornerstones.

1. Quarterback Jimmy Garoppolo. Seemed to work magic last season. Won five games in a row with a team that started 1-10. The 49ers certainly thought Garoppolo was a magician and a franchise quarterback, so they made him the highest-paid player in the NFL. But he struggled this season, lost two of his three starts, nearly lost all three and tore his ACL. Through eight career starts with the 49ers, his numbers aren't much better than Mullens'. Seriously. Mullens, 23, has completed 64.5 percent of his passes, and so has Garoppolo. Mullens averages 8.1 yards per pass attempt, and Garoppolo averages 8.5. Mullens' quarterback rating 91.5, and Garoppolo's is 92.6. Garoppolo is 27 and we still don't know how good he is. He could be overrated, or the next great 49ers quarterback.

Group 6: Legitimate franchise cornerstones.

1. Defensive tackle DeForest Buckner. The best 49ers player since they drafted him in 2016, and the second-best defensive tackle in the NFL this season after Rams DT Aaron Donald. Buckner has nine sacks — a career high — and there are four games left. He's a lock to make the Pro Bowl.

2. Kicker Robbie Gould. Has made 62 of 65 field-goal attempts since the 49ers signed him in 2017. Turned 36 on Thursday. Still young enough for a kicker.

3. Fullback Kyle Juszczyk. A two-time Pro Bowler who should make his third appearance this season. Averages 11 yards per catch this season, fantastic for a fullback. Bourne, a wide receiver, averages 10.9 yards per catch.

4. TE George Kittle. On pace to gain 1,191 receiving yards this season — third most in the NFL among tight ends. Kittle is an ascending player and the 49ers' one new cornerstone this season.

So where do the 49ers stand? If you combine groups 3, 4, 5 and 6, they have the beginnings of a legitimate long-term roster. The beginnings. They still need, to name a few, a left tackle, wide receiver, cornerback, free safety and outside pass rusher. The search continues.