I think it's a combination of conditioning and lack of extended repertoires. Some more of one than the other.
If we can't ever get these guys to go 75 pitches in a game, then we have to maximize their chances to do the best they can by not putting them in those situations, anymore.
I've been ringing the bell for adding two major studs at the TOTR, but in reality we probably need 2 plus some rotation depth to insure we never have to start Houck, Whitlock and probably Crawford, too. I think Pivetta can be handed the 5th slot, but we need more depth than Sale to make sure those 3 stay in the pen 100%. Sure, use them as openers, if needed, but never let them go beyond about 50 pitches or 18 batters- EVER!
SP1 FA
SP2 FA
SP3 Bello
SP4 FA
SP5 Pivetta & Sale
(Add SP ML ready depth to minor leagues)
Closer Jansen
Set Up Martin, Wink, Schreiber, Joely/Bernardino
Long Relief Houck, Crawford, Whitlock
Minor league depth:
SP: FA, FA, Gambrell, Hagenman, Wikelman, Drohan
SR: Kelly, Robertson, Guerrero, Mills
LR: Murphy, Walter, Van Belle, Song