Why won't a 4.6" display ain’t gonna cut it if Apple is selling tons of new iPhone 7 and 8 with a 4.7" display and even selling the iPhone SE until recently with a 4" display?
Two words... aspect ratio.
You can't just look at the diagonal size in inches when the screens are different shapes.
4.6" doesn't sound too far from 4.7" and 4.0" in numerical terms.
But when that 4.6" is also a skinny 21:9 aspect ratio... it makes quite a difference.

