No, it is lock in. If apple allowed for multiple app stores other than their own, then users could pay for an app on one app store, and then not have to pay again on another, potentially even on non-apple devices.
I encountered this when I first purchased minecraft bedrock edition on the amazon kindle. Rather than repurchasing it on the google play store when on a non-amazon, I simply tracked down the Amazon app store for non-amazon devices, and redownloaded it from there. No lock in to Amazon or other android devices, both ways.
Now, the Apple app store would still probably not work on androids... but now they would actually have to compete for users on the app store, by offering something potentially better than transferable purchases across ecosystems.
I suspect the upcoming Epic store for iOS and android may be like that... pay for a game/app on one OS, get it available for all platforms where you have the Epic store. But the only reason the Epic store is even coming to iOS is because Apple has been forced to open up their ecosystem.