Kentucky is absolutely more talented than Missouri. I don't think that's up for debate. If we're looking at recruiting rankings, UK's average class from 2015-21 was, on average, six spots higher than Mizzou's average class (No. 33 to No. 39). It's one thing if you have one or two classes that are better, but if over seven years you're on average six classes better, that's quite a discrepancy. Also, MU's classes over that time came in a wide range, as high as No. 25 and as low as the 50s. UK's classes ranged from No. 25 to 38. The Cats have been way more consistent.
UK's experienced transfers are better players and came from Power 5 programs: Levis (Penn State), Robinson (Nebraska), Rosenthal (LSU), compared to Mizzou's transfers from Rice, Tulsa and Montana State. (MU also has Mookie Cooper from Ohio State, but he never played there.)
From 2015-21, Kentucky signed 27 four-star players.
Mizzou signed 12 - and just five who are still on the team. (This is per 247Sports.com's national composite rankings - so, not just one site's ratings.)
As for the scheme or talent question, I brought up some of the NFL-to-college transition issues that I think might be factoring into the struggles. But more than anything, this appears to be a talent issue. Let's not pretend that all these Mizzou D-linemen returned to college because they love the college life so much more than what they could be doing in the NFL. There's just not obvious NFL talent on that line.