You don't own your data on a blockchain because everyone running a node gets access to it. Once you publish the data, it's fair game.
Only if the network says so. I assume you are talking about blogging combined with optional tips here. If you were talking about an RPG game you'd for sure own your character and all the items you farmed and everything else, and you'd be able to sell them at a profit without having to worry about tips. You'd get paid the fair market price (better or worse depending on time, supply, and demand).
If I send Bitcoin to someone... everyone gets that information, but all that information says is that I transferred Bitcoin from one person to another.
Ah whatever you know all this already. People do overhype blockchain and act like it's a silver bullet that's going to solve all problems. No argument there.
Data ownership is about access and privacy. So, a user having the power to share their data in different ways. Maybe they share only with a group of trusted friends via encrypted messages. Maybe they share the keys to that information with a little more. Maybe they would rather not risk the encrypted data go to certain people, so they localize how that data is released. The information being referenced here is rather general -> data where personal access control is desirable. There are some use cases where certain assets may be completely desirable not to be transparent, yet utilize encryption, security, and decentralization to make certain guarantees on that data.
I'm fine with Bitcoin transactions being public and global as that transparency enhances the product and allows anyone to validate the public state of all Bitcoin which is important for being money, but other things outside the money domain perhaps not so much.