Videos on YouTube are selling advertisements so wouldn't this apply here?
1. It's parody. Parody has specific statutory protection.
2. It's clearly labelled as speech synthesis.
3. It doesn't stand in for any of the original works. The market for deep fakes is much different than that for songs or presidential speeches.
It's really not clear to me. This page cites a case where someone imitated Dr Seuss' literary voice and lost.
It's one thing to impersonate someone to make fun of them, but he's not picking texts for them that way. A Bush impersonator reading the phone book isn't obviously parodying Bush unless he starts throwing in comedy Bushisms or exaggerating the voice for effect. Some Elvis impersonators are parodying Elvis but a lot are just doing a straight recapitulation of his look and voice.
IANAL but I think the argument can be made that YT are the sellers here and they are protected by the DMCA