The point is that only you yourself can send any notes under your npub. And you cannot be censored. Even if a relay censored your notes, you can just go to another one.
So yeah, you own your data in the sense that it cannot be taken from you. But not on the sense that you can keep others from accessing it. (except private DMs)
Is something like my ip address also public?
If you use a VPN, no. If you don't, then you're trusting the relays not to collect your IP and use it against you or share it.
Collecting your IP is not part of the Nostr protocol, so there's nothing stopping you from taking steps to prevent it. And if someone does take those steps, they're competing with those who don't take those steps.
The market will ensure there is always optionality and Nostr is open for all to build on and use however they see fit.
Not normally to other clients, but the relays can see your IP address, yes. There are also some other possibilities, like sending someone an image that is served by a server you control.
On the other side: Of you use Twitter/X, Facebook, etc., they can always see your IP address. If you must hide that, then you can use Tor/Orbot for example. The #Amethyst client has that built in for example.
