What Apple is doing now is similar to what Microsoft did in the 90s regarding Internet Explorer. Yes, you can use other apps, but much of the common ways to integrate into the OS are purposely disabled for non-Apple apps for obvious anti-competitive purposes; for Google maps, you can't set it as your default maps app (which means Apple Maps is constantly opening in contexts where you obviously want Google Maps), there is no CarPlay integration, can't use it properly with Siri, etc.

I guess they can get away with it because iOS isn't a monopoly, but I think it's a dumb move on their part.