As my uncle comment suggests ( https://news.ycombinator.com/item?id=27426639 ) it's not clear cut. Just because you hit ctrl-c then ctrl-v on an asset doesn't mean what you're doing is automatically copyright infringement, it might be fair use assuming you changed something to a point where it's a derivative work based on the original work.
> the music rights-holders (not the anime rights-holders, interestingly...) will then claim all the monetization on those videos.
This is a Content ID Claim, and it's a system YouTube themselves made up so that companies can automatically start garnishing monetization earnings on videos that use their work in any capacity without having to do DMCAs themselves. In no way is this tied to copyright or fair use.
Pretty sure copyright doesn't at all work like that. I.e. copyright can be (and usually is, AFAIK) preserved across derivation.
Contenting ID it _totally_ about copyright. The only reason Google built it is to reduce the exposure they have to claims of copyright infringement, by easily (way too easily it turns out) allowing rights holders (or anyone claiming to be one) to post-fact claim earnings from infringing use of copyright material. Just because Google demonetises your video and sends a share of ad revenue to Sony/Warner/whoever, that doesn't mean you _didn't_ infringe copyright.
Nor does it mean you did infringe copyright. There's no direct correlation between one and the other. You can't use the function of Content ID to infer things about how Copyright works.
Content ID may be ABOUT copyright, but in no way is it TIED to copyright.
Artists use reference material all the time, and as long as the new work is the product of the new artist, it's all good. But directly copying art and then modifying it is still copying copyrighted material.
My understanding is in the music remix world, if you want to feature a song in your remix, you should get a license.
Similarly, my brother makes AMV videos and as I understand from him, the music rights-holders (not the anime rights-holders, interestingly...) will then claim all the monetization on those videos.