Yes but user data can be securely accessed between these services too, and fingers crossed the trust mechanisms allow that access to be on a needs basis and incentivised without copying

And how is that „secure” achieved. As soon as someone reads your data and has it in their system - poof, the promise of security is gone.

The most common answer to this problem given by the people behind this is „but there is a legal contract backing the data exchange and the governing body”. Nothing different than what we have today.