Being something carried means you're comparatively and significantly better than most people at something. But when 9 out of 10 people say they're wave carried then the numbers don't add up, not because they are lying about their skill, but because if everyone is that good at wave then you're not comparatively better than the majority, you're just part of it.
Edit: While I did make a mistake saying that being carried relates to other people and not your skillset, it still doesn't make sense. When everyone else considers themselves so much better at wave than other gamemodes then that skill becomes standardized. Who knows, maybe we need harder nine circles levels.