If the non-app-store-installed apps are sandboxed then they cannot actually run everything that tinkerers want and the same criticism persists. The "we don't own our phones" crowd wants root.
That's a different complaint though. Just allowing sandboxed, sideloaded, apps would enable a whole host of new apps such as emulators, plus it would allow apps to provide their own monetization (e.g. Fortnite).
There’s a far larger number of iPhone users that either don’t know what root is, or don’t care. And your parent post is incorrect, Apple denies apps all the time.