That's false. They use FT% when trying to project a player's jumpshot that hasn't yet translated in college. Like JJJ who hasn't shown to be a good shooter yet. So when you claim he has "catch and shoot potential", his FT% would be the first indicator scouts would look at. 78% isn't bad, but it also doesn't scream untapped potential either.
Kessler was drafted for his 3 and D potential. You need to do both, or be absolutely elite (like All NBA levels of elite) at one of those skills if you can't do both. JJJ has shown to be solid at one and underwhelming at the other. If his shot doesn't develop, then he will need to be the best perimeter defender in all of college basketball to get drafted.
As for your Davion Mitchell comparison, Mitchell can play the point and run your offense. JJJ can't do either of those things. There was a lot more to his game and how it translates at the next level.