In addition to being crippled under the hood, as other comments have pointed out, the alternative browsers cannot offer any extra features.

Want WebMIDI? Want push notifications? Sorry, you can't have that on iOS, not with any browser.

All browsers on iOS use Apple's WebKit browsing engine. Even alternative browsers like Chrome and Firefox on iOS are using WebKit instead of their own corresponding engines that are used on other platforms like desktop and Android

This is a point so horribly misunderstood that I seriously had dinner a few weeks ago with someone from the Mozilla Foundation who asked me the same question as they somehow didn't understand that Firefox Focus wasn't actually Firefox. It was in that moment I realized that we're doomed: Apple has managed to control the narrative here so ridiculously well by making it seem like alternative browsers exist, even when they don't, that more time has to now be spent continually re-educating people about what a browser even is than explaining why alternative browsers are important :(.

my understanding is all other browsers on ios are just safari rendering wrappers with various skins, menu bars, and addons