Whether there are more beneficiaries than advertisers or other mega companies is another easy one to answer: sure, people benefit more than advertisers/epic/etc by being able to use RCS (or hopefully iMessage) across platforms, as do other areas of opening up the Apple ecosystem. Does this hold in every case of opening up anything? Probably not, e.g. requiring the permissions model be allowed to have alternatives would very likely benefit shady actors a lot but the users extremely little.
Your last point is, in my opinion, the much more lively and core debate: at which point is the ecosystem opened the right amount? For me, still a bit farther than this, but not infinitely open.
As for which brand ecosystem for me: all the above. Windows for home, Linux+macOS for work, iPhone for phone, Android for tablet.
That's why it being actual free market competition where consumers have a choice is the real test. If 100% of people on iOS want to stick exclusively with the Apple App Store, then it being forced open won't matter because all other stores will fail when no user installs them.
On the other hand, if users are willing to use those other stores, maybe iOS users don't actually care about using exclusively Apple's App Store. Then the only one who benefits from blocking that is Apple to charge their extra fees. Look at their reasoning for removing Fortnite from the store: because Epic added an additional payment processor that wasn't Apple. It's not like they removed Apple payment as an option either. So users had the benefit of more choices!
> even if it is still far from where it should be.
Where do you reckon it should be? Do you think they should let developers do/access whatever they want, or do you mean something else? Do you personally use an android or ios device (or maybe some niche os)?