This is more anecdotal than anything, but I've noticed that teams have had some decent success selecting college pitchers in the early-20s. There usually are one or two college starters than fall for some reason and yet have provided good value for their teams. As some recent examples, Stroman, Wacha, Weaver, Beuhler were all drafted in the 20s. All could have been drafted higher, but each had an issue (size, lake of third pitch, injury concerns) that caused them to slip. Even going back further into Twins history, Gibson - as much of a roller-coaster ride it has been with him - has provided excellent value for the #22 overall pick.
I hate to nitpick, but Wacha went 19th overall, not in the 20's.
But I'm seeing some comparisons between him & Kowar.Wacha supposedly fell because he had a limited repertoire, I believe the same as Kowar-fastball/changeup.
And I lied.I LOVE to nitpick :-).