If there is a single customer, it is not a monopoly, but a monopsony:
> https://en.wikipedia.org/w/index.php?title=Monopsony&oldid=9...
Would the "average" Google employees really care about this? I would rather imagine that only executive level employees of Google could be happy about this. And these people play much deeper political games than caring about a wrong word.
Killing small businesses definitely counts as a market distortion. Good luck arguing it doesn't.
And there is no competitive service, because YT is an audience provider, and not specifically a video hosting provider.
In fact these problems would go away if YT offered a paid tier - with proper support - for content providers.
But YT and Google are averse to treating anyone else as an equal partner, so that's never going to happen.
Yes, this is the monopoly part of the argument. There are no real and practical alternatives for content creators, it seems.