The problem is that, at least in Europe, the intent of the law is evaluated just as strongly as the letter of the law.
So, if we got this law that very clearly says it shall be easy to technically and effectively install third-party apps as a user, and also contains provisions that say third-party apps must get the same API access first-party ones get, it would be ridiculous for a court to reach the conclusion that it's acceptable for a developer to still be subjected to Apple's whims, except now they're being screwed inside their own infra!(tm)
So, if we got this law that very clearly says it shall be easy to technically and effectively install third-party apps as a user, and also contains provisions that say third-party apps must get the same API access first-party ones get, it would be ridiculous for a court to reach the conclusion that it's acceptable for a developer to still be subjected to Apple's whims, except now they're being screwed inside their own infra!(tm)
Law is not code.