My man Joe Posnanski had a very good article relating to the effect of closers on teams winning the game when leading entering the 9th inning. It turns out that the % of times a team wins the game in this situation has remained remarkably consistent throughout the years (95% overall, but he also broke it down into 1 run leads, 2 run leads, etc.), regardless of the changes to late inning pitching philosophy.
Here is his summary:
"But I just find it fascinating that no matter how much everyone tries to fiddle with the last inning of a game — closers, match-ups, specialists, pinch-hitters, whatever else — those overall ninth-inning win percentages just do not move. I would guess that teams with great closers having great years might help a team squeeze an extra win or two in a season. Maybe. But I do wonder if all of the ninth inning tactics are about as useful as rearranging furniture."
Full article here: https://joeposnanski.com/the-closer-you-get/