If every store had to make every app available, then sure I'd have choice and maybe that could be super cool.
But nobody's talking about that. We're talking about a world where major corporations will make their apps available only through their own stores and can refuse to do refunds and make canceling subscriptions a nightmare.
I don't see any increased choice at all. All I see is corporations forcing their own stores, that will probably be far less consumer-friendly, and users won't have any increased choice at all.