I think at times fans overrate the things they can see (small on-field decisions) and underrate things they can't see (keeping a happy cohesive locker-room, man-management, working well with players behind the scenes on a day-to-day basis) and the result is you get fans screaming that the manager sucks because he made the slightly wrong small decision, while ignoring the bigger picture.
But some of the decisions Montoyo makes are just mindnumbingly stupid and don't speak to his being someone who has a competent grip on what's happening on the field in front of him. I try to like Montoyo and then you see something like this and it's just like ... WTF. And it probably didn't cost the team the game today, but when you make 15 or 20 of those decisions over the course of a season, it will start to cost you games.
OPS vs. RH pitching, 2020 :
Joe Panik : .590
Danny Jansen : .789
Alejandro Kirk : 1.265 (albeit obviously in a small sample size)