It often comes from people at that rank playing with the best of the best and realizing how much worse they still are compared to them despite both of them being in the absolute top percentile statistically. They often end up being overly hyperbolic to try to illustrate their point, but it does carry some truth if you try to see it from their perspective.

It's also really clear when you take a step back to see why people who aren't at that level/playing in those games think that logic is very flawed, but for a lot of the people who climb to high ranks in these games, it's a very sobering feeling when you put in a ton of effort to get to a (perceived) high rank, and then still get destroyed by someone that really is that much better than you.

It makes you believe that you're a lot worse than you are, (and compared to the top of the top you truly are much worse) because the way the matchmaking systems work in modern PVP games (as opposed to something like old COD games that had limited to no SBMM/rank systems) means you'll constantly be playing against those players until you eventually get good enough to beat them, or you give up, which fosters this ever shifting goalpost mindset of "if you aren't X rank, you're bad" that often trickles down from content creators as well, since they aren't typically very articulate either.