Commanders were basically a more advanced form of control groups that allowed some nifty stuff, plus a fairly good tank on their own since they came with tons of HP. Also repair turrets are a thing and they're pretty good for keeping an army alive a bit longer when needed.
Also Robsoie, you're doing it wrong dude, you don't need early units, just rush out with some trucks and build walls in chokepoints. Early on they're tanky enough that a single truck can sustain a wall against a dozen enemies without much trouble, and they're way cheaper than any amount of units you'd need to defend against the early rushes. This in turn allows you to tech up like crazy and get some stuff like mortar emplacements which then allow you to just start pushing out from the safety of your walls with zero risk. Just try and do that in a timely manner, before the AI gets their hands on planes and starts harassing you constantly, won't be doing much damage at first but they're fairly hard to get rid of unless you teched into a decent amount of the AA weapons.
As for the game itself, yeah, this thing was so goddamn far ahead of its time that even now, over 20 years later not a single RTS has approached the level of complexity and replayability of this thing. A handful have tried and some were ok (The early Earth series get an honorable mention) but none have manged what this game did. Amazingly enough, this thing had a PS1 port, because that's how I bloody found out about it, a friend had it and I played it at his place all those years ago, then went on to find the PC version was a thing and jumped on that shit fast and hard.