Haven't a substantial number of creators turned towards sponsorships and embedded advertising because they felt like YouTube was being too capricious with their monetization policies?
yes, but those creators typically don't turn off youtube monetization. they just decided they wanted even more money than they were getting from youtube ads.
They effectively can't turn off monetization and get any benefit from the platform. YT doesn't promote non-monetized videos so they may as well be unlisted, cuz that's how many views they'll get. Which I think is fair -- it's a free service, if Youtubers want free promotion it's fair for YouTube to get their beak wet with some of the profits from the video.
and the downvotes on this comment prove it's working. nobody wants to believe that their favourite youtubers are actually the ones who want all these ads, it's much more comfortable to blame the big evil company instead.