Even in the future if they are required by law to provide it, I wouldn't bet against the craftiness of the providers to invent some sort of network effect dark pattern to make it painful, if not outright impossible.
Just as an example, with Muse I can already see that the way they are thinking of making money is via taking a transaction cut, so it's not that hard to imagine that Meta can negotiate deals for txns that happens through Muse which won't be available elsewhere.
Your second point is where I'd imagine the future moats to live: Exclusivity deals with service providers. Things are already in motion with Amazon banning and Shopify explicitly inviting Muse; we'll probably see much more of that.