There’s a big gulf between “irreplaceable” and “not justifiably replaceable at the moment”.
Like I said in the game-thread yesterday, while I’m something of a Foltynewicz defender, I also think it’d be smart to shop him this offseason, assuming he continues to have a pretty good year (last night’s clunker notwithstanding)—especially seeing that his salary very likely could double in arb. But I also don’t think there’s anyone forcing him out of the rotation this instant—certainly I don’t think we’re at the point, with either player, that Fried should be inserted and Folty demoted—nor do I think he should be jettisoned for for the first flotsam that comes knocking.