. . . body types, although not sure that matters. Some excellent hefty guys lasted forever - CC, Wells, Colon, Tiant.
I think if Feliz stays healthy there is absolutely no reason he can't pitch well for a long time. So much of his success comes from the suppleness of his hand and wrist. He can impart enormous spin without much physical effort so losing speed won't hurt him as much as it might others. His fastballs have always been his worst pitches anyway, almost from the beginning. Of course, that same spin can make the pitches uncontrollable. Look at some of those pitches on off-speed.com - it's astonishing how much trouble Jaso has holding on to the ball. It just moves so much.
Sutton was a control artist not a stuff guy. That said, I think Felix's model ought to be a guy on his own team - Kuma. If he ever throws a fastball that catches more than an inch of the plate it was a horrible mistake. Feliz will never be that fine but with his stuff he doesn't have to be if he uses the fastballs as a tease, not a weapon.