Who defines what is "best experience"?
Good for you.
However the world is bigger than you and the first thing I would customize if I had an iPhone: Replace the default browser with Firefox, because that's the only browser which has me covered. Except you're not allowed to do that. It can't be done.
That's a score 0 for something which matters a lot to a lot of users: being able to use their preferred browser. And that's definitely a customization.
In fact if given the options I'd probably mess with them and negatively influence the experience.
Pardon me for saying so, but saying anything like that just makes you sound like an apologist, a shill. It instantly makes you 200 times less credible.
That's just uncalled for. Can you not perceive that the very same can be said of ”…the first thing I would customize if I had an iPhone: Replace the default browser for Firefox, because that's the only browser that has me covered." comes off in exactly the same manner? The last part comes off as marketing speak to me. Are you an employee of Mozilla, paid or otherwise? As to reducing credibility; petty passive-agressive name calling lowers yours immeasurably.