Your proposition of 40/hr inside would put a preloader @ 42k/yr minimum.
It would close the revolving door & bring in better workers but eventually every inside position would be filled with people who only want to work 4 hours a day & still make a decent wage.
It would stagnate the crop of potential drivers & they would have to hire them off the street.
Ups needs the revolving door so they can pick out the better workers & dangle a 6 figure income in their face until they need them to drive.
$40 an hour for inside workers would be a minimum of $80,000 a year
The hourly wage is only part of the problem
The part-timers do not realize how much the benefits cost
If you want to make the big bucks then you have to go driving, bottom line