"Gatekeeper approved by Apple" is not entirely accurate since Apple also gatekeeps what that gatekeeper can actually approve. All apps in third-party app stores must be notarized and Apple has complete control of what apps get notarized. UTM for example is not allowed on iOS even on third-party app stores since Apple has denied them notarization.

It's more of a choice between Apple, or Apple + third-party gatekeeper. Well, at least now – I fully expect this to be investigated by the EU.