I am a lifelong controller user, and I will use it over mouse and keyboard 99.9% of the time. Even in cases where it puts me at a disadvantage. But that’s the thing: it often puts me at a disadvantage. There isn’t a controller in the world that can match the precision and speed of a mouse. Simple as that. It’s why they have the distinct advantage in FPS’s. It’s not really an opinion, it’s pretty easy to measure.
Ultimately, I think your framing is also part of the issue here. You are acting like people are saying “controllers are unusable on PC” when the reality is when people are saying “don’t use controllers” they’re saying “because they put you at a disadvantage.” That’s what they mean by “bad for FPS games.” If you want to win more, you need to use a mouse and keyboard. Simple as that. If that doesn’t matter to you, then no one cares. Unless they are stuck with you on their team and you become a liability, which I think is a very valid objection.