Number of players drafted and still on the team

[*ochocincos*]

Let's assess specifically the 2019-2021 draft classes, as we've seen them in the league for 2+ years now, so we should be able to assess success decently well.

2019:
Pratt took a couple years to get going, but he finally came into his own the past couple years, and he (surprisingly) re-signed with the Bengals on a new veteran contract. He's become the best of the 2019 draft class so far.
Jonah has been a good OT at times, a decent one, and a bad one. It's not great for his potential suitors this coming offseason that he got moved out of LT spot, but he may end up thriving at RT this season and land a pretty good veteran contract with the Bengals or someone else because of it.
The other guys are just perennial mediocre backups or off the team.

2020:
This was the home run draft class. Probably no coincidence the Bengals also picked first, giving them the best chance to grab talent.
Burrow, Higgins, and Wilson are very good, if not great.
ADG is a solid rotational guy, but I don't think he'll ever take over primary defensive snaps unless an injury occurs. He might have to go elsewhere to get more opportunity.
Bailey, like ADG, has become a solid backup.

2021:
Chase is a stud, but he's been about the only guy to show much to this point.
McPherson has been a great kicker selection.
Carman's only decent play has been at LT, and there's been a better/more experienced guy in front of him this whole time, so he's not going to get much playing time there unless injury occurs. It wouldn't surprise me if he's not re-signed when his rookie contract ends after 2024 season, if not let go before then.
Ossai was plagued with injury his first year, put up a few sacks last year. He could potentially turn into something toward the end of this season, but he's nothing more than a decent backup right now.
The rest are just perennial mediocre backups or off the team.

So out of 27 picks, 6 have been true hits so far - Pratt, Burrow, Higgins, Wilson, Chase, McPherson
Jonah has been ok, but not lived up to his draft status.
So you're looking at 22-26% of the picks in that window have been good, depending on your thoughts on Jonah.
From an offense/defense perspective, every hit has been a Day 1/2 selection. They haven't really had any diamonds in the rough emerge from Day 3 yet.

While I'd like to see a couple Day 3 offensive/defensive picks emerge into decent-or-better starters at some point, at least they're having pretty good success on early picks. It was those early picks that doomed the latter years of the Marvin era.