Once upon a time there were 9-inning SPs and 3-inning closers, until — prepare for deep and thoughtful analysis here — there weren’t. Tony LaRussa once took a two-time 20 game winner, with a no-hitter on his ledger, and turned him into the league’s most dominant “one inning closer”. Since then many teams have followed suit, spinning their failed SPs into plus relievers.
Every era (not ERA) has its understood “way we do things” and with baseball tending to be old school, change tends to evolve slowly. Yet eventually change still occurs because once someone not only says “launch angle!