I know it sucks but in the worst case if you really need a quick fix, Android ebooks readers like "fullreader" will read your existing ebooks through the android TTS
I tried searching for another app using better quality voices (some do use amazing AI voices) but they're of course not free and I couldn't find a working cracked version as they use a remote server for the AI
It lacks the tones and quality of a real voice actor, but until you find a reliable source...
They are aware of it I guess, but probably don't deal with the issue in an effective way.
There's a French channel I look at, they make sponsor sequences as well but I don't skip them because they make those in such a bizarre, ridiculous and remotely funny way I'm even curious to see how bad the sponsor sequence is gonna be.
They alone are the only reason why I set up my sponsorblock to not skip sponsor sequences, but to skip everything else