Coach was all over Big Lou for quite a while in his career noting that his "work-rate" (number of plays consecutively and total plays at maximum level effort per game) was so low --- in Kelly's eyes --- that unless Lou got his physical act together he wasn't going to play at all, even if he was great for 10-15 plays. Lou at least got that part of the message and got in the line-up.
As to Ewell: my brother (the US National Olympic Weight-Lifting coach, Tim Swords) says that players like Ewell (he wasn't talking to me specifically about him) can increase mass/weight and explosive burst (including overall speed, jumping, quickness) by following proper Olympic-lifting training (including heavy squats.) He has some very "odd-shaped" studs who can sky, for instance. ... and he has helped put dozens of wannabees into D1 football programs. Ewell could, with proper training, "easily" put on weight and explosion at the same time.
Doubtless Balis knows all of that already.