Would you. Consider seeing up defensive positions engineer jobs? Because pios can do that and CE cannot. Sandbags as well as bunkers (yes they cost extra but it's an option) and mines that can OHK light vehicles. Pios cost more because they do more. It's not negotiable. Do more= cost more do less =cost less pios do more = cost more CE do less = cost less. There's more to the game than JUST repairs late game.
The sandbag argument doesn't hold water.
The mainlines that don't get sandbags/green cover have it on their engineers instead. Pios having sandbags instead of the mainline is a serious disadvantage, and you're misunderstanding it as an advantage. It's the same case for Rifles, except that Rear Echelons have significantly less duties - no repairs, no base-building, no anti-garrison (disadvantage actually).
I've always found it necessary to get a relatively early second pio since repairs/wires/mines/sweeping/cover building/anti-garrison/base-building duty require 2 pios combined.
I'm quite sure grenadiers would actually start being pretty good if they could build their own sandbags to protect themselves instead of getting roflstomped the moment allied infantry appears.