Yup, if I want to level up my units, I'll research upgrades for my units. That requires resources, not combat. I honestly never saw the point of a mechanic or medic in C&C, because if I won a battle, I would usually go on to destroy their infra, not heal up to go again.

Starcraft got this right.

One thing that may be interesting here is a "drill" feature, where you lock up a unit for some time and expend some resources to get a higher tier unit. That way you can spam units early on and replace them later for cheaper, but the total cost would be higher than building that unit initially.

I bought the C&C collection because I loved it when I was younger. EA fucked up C&C3 with an update that turned it into a constant zerg rush by the AI and Red Alert 3 has the same bullshit AND a shitty AI co-commander blowing through resources while doing fuck all. There's no strategy, just frantic clicking and attack alerts.

Wasn't that going on as far back as WC3? If I wanted an RPG I would have bought one.

Warzone 2100 did the RPG elements as much as was needed in a RTS. Sure individual units gained XP,.and they carried over from one mission to the next. You could also recycle units to upgrade their chassis. That was it. You could also just churn out basic troops and just throw away armies if you wanted.