to be honest the splatoon comp scene has genuinly been the most positive and friendly one I've ever experience, and this is coming from the person that's played TCGs and other very nerdy hobbies that attract similar introverted people usually.
I think the people saying that the comp scene has too much whining or negativity haven't actually interacted with it, or take a difference of opinion as dismissal of concerns/active hostility towards their views(I know when I used to be deep in the yugioh comp scene I got annoyed at more beginner players asking the same 3 basic questions non-stop in help channels sometimes, but its rarely out of active malice or looking down on players less experienced than me, it's just exhausting.)
At the end of the day, The more hours or general investment you have in a game, the more likely it is you are to play the game to an above average level, and, more importantly, have a better understanding of the game from raw experience(this applies to single-player games too.) From my experience, the divide between the casual invested with only a couple dozen hours, and the comp players with 500-1000 hours is steep simply on that experience divide alone; because the comp player sees the game for what it actually is from their experience delving into the deep side of the ink, while the casual player has not experienced even a half of what the comp player has and might have formed opinions around misinfo/exaggerations/other misc logically fallicies(I though Anarchy Series was a "do it once, if you lose, you can never que up for it again" mode until I got into the comp scene, as a personal ancedote)