I get to use Firefox, it comes with nice tracker blocking out of the box, it keeps my history in sync with my other devices and I find the UI to be a little nicer (personal taste).
Of course I'd like the Firefox that's available on Android, with extensions capabilities and web push support. But having the ability to open links from Mail in iOS Firefox would still be nice and I can't wait for it.
Neither situation is perfect, but the browser's rendering engine is surpassed by other priorities when choosing a phone.
I do look forward to the day I can use something like Pine as a daily phone though
Syncing bookmarks, UI, tab handling etc tend to be bigger pain points for individuals, as opposed to the more dev-focused aspects such as supporting a certain API in Javascript.
- Extensions support, so uBlock Origin, Privacy Badger, the best ad-blocking combination that far surpasses Safari's content blockers, which are pretty shitty; and extensions are useful for more than ad-blocking — e.g. I have another one on my tablet that turns all web pages to dark mode, whether they support it or not
- Web push notifications
- (Up until very recently) webp format support
On Android I wouldn't even install many apps, like Facebook, or Twitter, or Fastmail, I'd simply use them as PWAs (web apps), in Firefox with ads blocking on, because I could.
I still use Firefox on iOS for the history / bookmarks syncing, but it's a shadow of actual Firefox.
Except that for many/most people it's equally important to have a market choice which drives product improvements by competition. Not being able to choose a fully opensource browser engine (not even Firefox!) on iOS is a severe blow to opensource as a whole and browser engine competition in general. It's way worse than it ever was in times of IE6 - you never needed Microsoft's private signing keys to switch to Firefox or Chrome.