There are three problems Rocco has that make him a mediocre manager.
One, brain lock. Sometimes, when the game speeds up on him, he locks up and can't make the obvious call. Examples of this are when he fails to put in a pinch runner or replace a struggling reliever.
Two, galaxy brain. More or less the opposite of brain lock, this happens when he has a long time to think about something - like when he's going to take his starter out of the game - and he focuses too much on one aspect of the game and talks himself into a not-great decision.
Third, uninspiring leader. This is his failure to get his players to play smart, hard-nosed baseball.
Anyway, this was a case of galaxy brain. The question he asked himself was "Who is the best pitcher to get Duran out?" rather than "Who is the best pitcher to finish the inning?" - with the understanding that finishing the inning might take facing multiple batters besides Duran. If you ask the second question, the obvious answer is Zebby Matthews (assuming the high-leverage relievers aren't on the table, which I think is fair), because Irvin is a disaster against the upcoming righties. But Rocco disregarded that. He focused only on Duran and ignored the question of what happens if Irvin *doesn't* get Duran.
A simplified and also better question to ask would be "You can put your fate in Cole Irvin's hands or Zebby Matthews'. Who do you choose?" Given the evidence of your eyes yesterday, Matthews was the better choice.
Addendum: This is exactly what we got Irvin for! If you can't use him here, where can you use him? Exactly. That's why he was available on the waiver wire. LOOGies are a dying breed because of exactly this problem.