it doesn't matter, if GrapheneOS is going to be the only one to allow "side-loading", then the market for application installable without a store will disappear
As I said, it is useful for the users to have software that is complying with the latest version of the API, and it is good that Google is enforcing it
Because they want developers to use the latest version of their API. And as a user it is a good thing, as the API is getting more restrictive and privacy focused