Pretty sure the biggest victims of this were Rockapella (who apparently did every a cappella song) and Weird Al (who apparently recorded every comedy song).
Here’s how cool Al Yankovic is though: for years he maintained a list on his website of every comedy song falsely attributed to him and all the actual artists who made them. I don’t think it’s up anymore, there can’t be much need for it these days, but Al was very cool for doing that.
No pirated content is hosted on the instance. It’s just refugees from communities that already existed on reddit for years with no issues.