Agree with you but confused about
And at least half of those mobile users are on iphones, where they have no choice.
I use old.reddit on iPhone on Safari and it works just fine? I even have an extension to make it appear mobile friendly, so I'm really curious as what you mean by this.
Sink it for Reddit, which someone posted here on Lemmy (ironically). I can't seem to link it from the app store, but the icon is an anchor with a red-orange background! It's also completely free.