(googler, but i work on and far prefer iOS. i care about the platform and i wish it had actual browser engine competition)
FWIW I like Firefox or Chromium a hell of a lot better than Safari, except that both drop my Macbook's battery life by an hour or more versus Safari, and both feel heavier in terms of their effects on overall system responsiveness (the feeling I get is that Safari is way better at keeping JavaScript from stomping all over everything). I do use Firefox on Linux, if I'm on something beefy enough to use a really heavy browser and still be able to multitask.
For that matter, it'd be worth keeping other browser engines out if their integrations broke Apple's only-vendor-who-seems-to-give-a-shit accessibility features. I dunno, maybe iOS Firefox and Chrome already do, but I'd imagine forcing Webkit keeps people from embedding browser engines that screw with that. Which, again, wouldn't bother me if anyone else were half as good. Please, for the love of god, anyone, compete with Apple. No one is, right now.