> Is 80/20 ever generally correct?

Sometimes. But it, or 90/10, or sometimes 75/25, is understood to main “a large part of the time”/“a significantly smaller but still crucial amount off the time”.

> If you pay attention, so much user content is just repetition of something they read on the same fucking website and uncritically checked into their brain.

Which is exactly the problem. We now have LLMs doing the same thing, flooding everywhere with more of that noise, further hiding what good signal remains. Even if some of that good signal is by chance almost entirely LLM generated too, it appears to be at best a vanishingly small amount.