In theory, you agreed to all the ways they can screw you over when signing up. In reality of course no one can be reasonably expected to understand the full ramifications of multi-page terms of service.
I'm happy that EU is pushing this ownership argument forward. GDPR seemed unreasonable just a few years ago, now it's the new standard. I also don't think it's the final destination. We're moving towards more regulation, but that's expected in any mature industry.
However, this specific topic to me isn't as much about ownership as it's about redundancy and diversification.
Of course it's not a good idea to build your whole identity on some corporate identifier (@gmail.com, @icloud.com...). Of course your business income shouldn't be based on a single platform (e.g. youtube demonetization, facebook news). These problems could've been forseen even without the benefit of hindsight.
There's no such thing as absolute ownership anyway. Even your money or real estate belongs to you within the framework of modern banks and governments. Doesn't mean this ownership isn't meaningful, just that there are always limits and gotchas.
The most meaningful thing you can do is own as much of your digital surface area as you can. Having everything under your own domains will get the most bang for your buck. I don't bother with self-hosting, but for someone else that would be a must. Your mileage may vary.