1. Are 3rd party stores popular on Android? How about preinstalled vendor-run stores such as the Samsung Galaxy Store?
2. Small developers are the primary beneficiary of unified stores. On the desktop Steam is a good example of that, while large developers can afford the costs of generating direct sales via ATL marketing and support, small developers largely rely on in-store discovery/visibility to reach a larger audience.
3. However a Steam-like store hasn't eventuated on Android likely because Google's store is already good enough. Steam largely benefits from being early and maintains that position despite the numerous copycat stores having compelling offers (e.g. the Epic store is largely a dud despite regularly giving away popular gaming titles.)
4. If the final legislated position for Apple's App Store is simply to be a Steam-esque add-on store, i.e. merely a place of convenience but not at all necessary, Apple will no longer be beholden to accomodating hostile competitors.
5. The EU is still discovering how they can balance strict control versus existing commercial freedoms, and we're about to see this play out with Facebook. Since the EU has suggested that Facebook cannot charge for an Ad-free tier. Which has a few obvious run on implications, i.e. that a company cannot set the price of their own product and ad-supported "free" services (such as Google, etc.) are not in compliance.
6. Don't expect any of the "gatekeepers" to self-regulate their actions, because they can't read the mind of the EU. Instead they'll now sit and wait to be told what to do.
All of these thoughts obviously point in different directions, but there are some themes that apply to all of them.
1. Large software developers are pushing for independent stores because it benefits them, and protects them from disruption from emergent competitors.
2. Small developers will still need to rely on hive/halo visibility (i.e. Steam, Google Play, Apple App Store). Even though this costs them more than direct sales.
3. Either Apple has no control and thus no responsibility, or they have full control and can wield that against hostile competitors. There is no scenario where Apple has no control and full responsibility.
4. People don't like that last point, and that mental disconnect is on display - but that's where all of this takes us. It's a case of careful what you wish for.