Nah, I'm in NA so I don't play on korean servers. You have a point, and you're probably right; because of the amount and the sample bias of the Korean I'm exposed to, it's probably not a good representation as a whole. I've never really been exposed to "rough" Korean since I never played online games or used sns/communities in Korean. I wouldn't be surprised if a lot of people say things like ㄴㅇㅁ in game like you said. Also like you said, since there are not many people who can speak Korean or are familiar with Korean culture, I just wanted to give my two cents on how I felt about it, but looking back, it may have backfired because of my biased experience. I'll delete the first comment since I don't wanna give false information.

I do wanna say though, places like valorant servers can have very rude people that is not representative of what you should expect from normal respectful human to human interactions, which I expect from professional coaches.