On iOS, it is about the browser, as Apple is acting anti-competitive by not allowing any other browser engines but their own. Browser makers can't compete with Safari by making a faster browser for example, because they won't be able to deploy it on iOS device. All applications go through the App Store, and the App Store forbids any browser engines not made by Apple.
Regarding the app stores, it seems like lawmakers are catching up with the idea of "If I buy it, I should be able to own it and make my own decisions", which includes being able to install applications from 3rd party developers. It seems like a fine idea that Apple has a default application index where you can install applications from, but what is not fine is Apple deciding which application indexes should be allowed to exists in the first place.
Kind of like how lawmakers wouldn't look the other way if suddenly all macOS computers only allowed installation of software from the App Store. Purchasing a device shouldn't mean "The company decides what I'm allowed to install on this thing".