I don't follow how you're reaching your conclusion. You only mind reading AI content when it's obviously AI/slop and you conclude the vast majority of decent content is not AI generated. In your conclusion how were you able to identify good content as being written by AI or not?
E.g. it's perfectly possible that in terms of prevalence "AI slop > AI acceptable > human acceptable" instead "AI slop > human acceptable > AI acceptable" and nothing noted explains why it is one instead of the other.
E.g. it's perfectly possible that in terms of prevalence "AI slop > AI acceptable > human acceptable" instead "AI slop > human acceptable > AI acceptable" and nothing noted explains why it is one instead of the other.