How do they "own" it exactly?

Are they able to control people's transactions? No

They do influence the development of ethereum, however what's great about blockchain is that the community can "fire" the developers and choose new ones if they want. This almost happened after the DAO rollback drama in-fact.

Does someone with no money own any stake in Ethereum? I don't understand your point.

Why would you think Ethereum is supposed to be a socialist's paradise?