"Reachability", to be blunt, is an admission of defeat - and I know this is a tired trope - that would not have happened under Jobs. Sure, Jobs may have surrendered to the trend of larger screen sizes, but he would've insisted on something that wasn't so plainly awful as Reachability.
The bigger screen is beautiful and I love looking at it, but I hate touching it. I also hate the fact that the top right corner of all apps is now no-mans land, covered with touch sensors as a matter of obligation than actual usefulness. Expect app developers to start treating the top right corner of the screen as non-user-interactive space only useful for displays.
It's too bad that Apple evidently doesn't have any intention of continuing the 4" form factor. I'd like to have seen multiple screen sizes given priority.