All service providers above some scale should be obliged to create a transparent processes or be taken for external jusges.

Even better: all providers of services with more than 100K users or 10% of country internet users should be forced to provide API to export / import data in open format.

Maybe service providers above some scale just shouldn't exist, period?

It would be a lot harder to erect walled gardens if you're only serving a small subset of users - they would balk and leave at any attempt to prevent them from interacting with others outside of the ecosystem, and it would be a lot easier to do so.