Chrome is also one app, what's your point though? That Google will come up with more favorable app store on iOS? Hardly unlikely, given how much inertia people have.
I don't know if it's likely but there are a lot of big brands that can't get their apps on the Apple store for whatever reason, just like Fortnite and Chrome. With enough of them, alternative app stores will take off.
I think the biggest category is alternative stores.
