Sutter in his prime made good hitters miss worse than I’d ever seen. His splitter did things baseball hadn’t seen before. Eventually others were able to replicate it and have success and over time hitters learned to hit it. But when new Sutter was as dominating as Manny Rivera. Manny’s pitch never was well replicated and he kept it going for a longer career. Sutter had arm injuries before his stardom and thus a shortened career. IIRC the injuries lead Bruce and his guru, who’s name escapes me, to develop the splitter. Closers were just becoming a ‘position’ in his era and many were lamenting there only being one reliever in the Hall, Hoyt Wilhelm, a knuckleballer who pitched forever. Sutter was the obvious add from what then was a small pool of candidates.
Rollie Fingers was the best reliever from that period between the Hoyt Wilhem and Bruce Smith eras.
I think you have the description of that pitch reversed. That pitch wasn't developed by those guys with arm troubles. It's what actually shortened the careers of those pitchers. That's why you see more guys today who throw sliders and cut fastballs instead of splitters.
Mariano Rivera was the master of the cut fastball. He learned it by mistake in the bullpen one day while fiddling around with his delivery, and he rode it to a long career as the best closer in the game.