Tech illiterate Windows users seem to have no problems removing replacing Edge/Bing with Chrome/Google (which, if you've ever tried recently, is quite a painful process - though I suspect it's a lot less painful in the EU where the dark patterns would land them in hot water).
I think the App Store will only be able to maintain it's dominance in Europe if it's a better experience, for both users and developers, than any of the alternatives.
The improvements Apple will make to the store to protect their dominant position will be significant.