While iOS has a quicker update scheme as Android, it's nowhere near as fast as an evergreen browser.
If I look at https://iosref.com/ios-usage there's only half of the users on last year update and 15% of users lagging behind on a 2+ year old browser version.
So expect your average users to have a new Safari version ~1.5 year after it's been out. So the answer to that is no, it's not fast enough to be considered evergreen.