Your problem is you only know what you've experienced at Ground. There was a time when couriers had a two week class, had to have a cdl, were trained in handling haz and international shipments, had to write out airbills,, had to know others routes enough to run a sort, and so on. That was on top of having our day put on hold while waiting for freight, often having everything disrupted and having to run a fire drill to compensate. And we, as I pointed out before, drove the big vans delivering all the bulk along with meeting deadlines all day. Depending on the station we ran at least the morning sort but in some stations had to do the reload too.
What you may be somewhat familiar with is the dumbed down job with the customer doing almost everything now with the courier mostly quickly scanning a barcode with a much more advanced tracking device. Driving a smaller van. Getting pickups and messages directly instead of running back to the truck to check.
The company hired quality people back then, many with college degrees, because it took some wherewithal to be both athletic enough and intelligent enough to juggle everything. Now they just hire in large numbers knowing many will quit before long because it's a dead end job and not worth the hassle. Because by simplifying everything they made it possible to do more with less people. Less people however who must be constantly moving.
Your drivers aren't going to have to do everything we did back then, but with combined operations they're going to have more expected of them than currently. Let's see if you're able to motivate them to do more and yet still keep them without paying more.