The definition of monopoly isn't the absence of alternatives, it's the absence of significant alternatives, and the fact that monopoly distorts the surrounding ecosystem.

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.