Apple won't let full third party web browsers into iOS, all web browsers have to use the Mobile Safari engine underneath. Apple added ad blockers to iOS but will only permit them in Mobile Safari proper. Third party "browsers" aren't permitted to use the ad blockers you can install in iOS.
Admittedly, I'm quite ignorant of the laws related, but wouldn't this be grounds for an anti-competitive lawsuit (even if the App Store terms specifically say so)?
Those laws only apply to monopolies. Apple doesn't have a monopoly in any market segment, so they engage in quite a few anti-competitive behaviors that would be illegal if they were a monopoly. That's why Microsoft got in trouble for bundling Internet Explorer with Windows even though end users could install any browser they liked while Apple is free to require iOS users only use Mobile Safari or a browser UI running on top of Mobile Safari (Chrome, Firefox, etc on iOS).
