If you're going to assume Rotom and Skarm take damage throughout the match then it's only reasonable to assume that Pinsir takes damage while he sets up, putting him in KO range of brave bird and/or volt switch. But really, it's not hard for a well balanced team to play 5 on 5 until Pinsir comes out. Don't waste your Rotom if Pinsir isn't around.I am not ignoring anything. Volt Switch and Brave Bird wont ko (even after rocks theres only a pathetically small chance of it happening since pinsir starts 2x weak to it), while pinsir is faster and can 2hko before they can land a second hit. Pinsir is a late game cleaner, skarmory and rotom-w are walls, they are the ones that are going to be tanking a lot of hits through the match, its pretty easy to assume that the majority time pinsir will be much more healthy. The amount of pressure pinsir puts in the opponent is ridiculous because of the lack of more reliable answers for it and how it can actually get past the few ones that do exist. Skarmory and rotom are the one being pressured to death, not pinsir. If you choose to ignore this simple fact than youre the one being irrational here.
And tbh you don't even need a counter to beat Pinsir. I have a team full of mons that Pinsir can OHKO at +2 (Aegislash, Bisharp, Landorus, Tyranitar, physical mLuc) yet I've never lost to a Pinsir or even really been threatened by one simply because all my mons threaten him back, preventing him from setting up, and I have plenty of priority to finish off a weakened Pinsir in the event that he does win a 1v1.