Before Opera gave up and became another Chrome reskin, I had plenty of sites that would not work for me until I switched user agent. The exact same thing would start to happen to all non-chrome browsers (and hell, even some chrome browsers) within months of other engines being available on iOS.

If doesn't matter whether or not your browser works or is even good, if the devs for that website couldn't be fucked supporting anything other than Chrome you are done.

I am sure regulators will eventually mandate other browser engines be allowed, when that happens the most likely course of action from Apple will be to give up too and switch to Chrome, leaving mozilla to be dangled about so that everyone can pretend there is no monopoly.