The right thing for users would be to allow user choice, and for Apple to compete fairly.
Apple allowing third party access doesn't automatically mean user data gets hoovered up by OpenAI, Anthropic, etc. It just means users now get the choice, if they want to make that choice. Users could stay with Siri/Apple if they care about what Apple is offering, or choose to accept the risks and terms of service with other third parties.
The EU isn't saying "you must preinstall every competitors offering" its "you must offer the ability for others to hook into the same APIs to be able to offer their own assistant on par with the first party option."
The user still remains in control by virtue of their own choice.