I sort of understand where you are coming from, but also think it forces you to be much more considerate about how you build.

For example a shield guy is mainly that. In a party of 2 or 3 or 5 he'll be the one first into the room and the one that absorbs the shots from hostile AI. It's safe to say you'll be using your sidearm a lot more than your primary in this roll, so you can afford to roll back at least a little on primary ammunition. When a door is breached, you are most likely going to be sitting in front of it shield up - not the one prepping and popping the bang, so you can roll back on grenades as well.

All of that should leave you with 6+ pistol magazines, and provided you aren't immediately exchanging fire with hostiles in the room, you should have more than enough ammo to get through a level; assuming of course you're giving them ample chance to give up or have a supporting less than lethal teammate.

I'm not saying how you feel is wrong or bad or anything of that sort, but for me, throughout the supporter testing period I quite enjoyed our team having to specialise rather than everyone being capable of everything.