They do control the default app repository, so from the PoV of many users, at least with respect to apps, the two are pretty much equivalent.

There are Android phones sold at least in Russia without Google services at all. People use them mostly fine.

And no, it's not mandatory for developers to use Google Play. It's a bit more work to DIY your app distribution, but you get total independence in exchange. It's ultimately developer's choice to make.