There are magnitudes more OC on Reddit than Lemmy just by nature of their user base size. There are bots and reposts, sure, but Lemmy pales in comparison to the amount of OC on Reddit
I’ve noticed this when I used to lurk in subreddits related to what I’m most knowledgeable about. So much misinformation getting upvoted because it’s said confidently
If by a good chunk you mean <0.1% of their content, I agree. The majority of Reddit users did not care to migrate, and many that did migrate didn’t delete their old content