Is there also an added effort around making iOS work on the smaller screen size/resolution as well though?
If they can standardise those, they might end up with an easier OS to maintain once the Mini (sadly) is no longer supported
You can zoom the screen anyway.
AFAIK it's 360px wide, the same as on larger phones. You can of course enable an accessibility option to take it down to 320px width, which was the iOS standard for almost a decade and only stopped being a standard iOS resolution when they killed off the iPod touch.