Not everyone who purchases a phone is the end user. If I'm buying a device for my organization or for a child, I might not want the device to enable that choice at runtime. I want to make the choice at the time of purchase.
Don't worry. Restricting what's allowed in a company owned iPhone already exists throughout MDM. And that won't change because it's not your device after all.
I can have the coice of alternative apps stores AND still enjoy a curated wallet garden.
How do I know it works? Android is precisely like that.
You see Android users also like the choice of a curated system. Choice being the important word here.