>You don't own Bitcoin if you don't control the keys.
That's wrong, and obviously so. That concept is "possession" and not "ownership".
What they write in their ToS doesn't matter, it does not change fundamentals of porperty law. (Well, as every legal argument on the internet it depends on your jurisdiction and the jurisdiction of the coinbase, as coinbase resides in multiple)
> Coinbase securely stores all Digital Currency private keys in our control in a combination of online and offline storage.
And if you read the whole thing,
> supported Digital Currency
is mentioned multiple times.
[1] https://www.coinbase.com/legal/user_agreement?locale=en-US#1....