Its game balancing. You can't have a unit in game be able to do everything. C&C3 is an RTS, Real Time Strategy, not simulation, which is the main reason why they have multiple squad types doing what, in real life, be accomplished by a single squad.
I know, putting all the real capabilities of a rifle man squad would make game balancing a nightmare. However, what I meant was that AI could function a lot better even in the current installments. Why should I tell the peacekeeper squad "shields up" when they could figure it out themselves? Why do I need to specifically order almost destroyed soldier squad to the hospital when they could have the capability to do it themselves, given the freedom to do so.
That you can give waypoint orders for units and restrict their weapon usage the way you want is good, but was it too much to ask for a single button that would give unit a permission to return after certain hitpoints are spent?
And then the bane of all real time strategies, why is there a specific unit for conquering buildings? Why can't a rifle man squad do it? This would make the importance of the rifle men squads higher, and they would have a role till the end of the game (a welcome change from the tank rushes most RTSs give at the end). Then combat engineer would be able to do something what it would do in actuality, like constructing tank blockades and temporary bridges and clearing mine fields.
Oh, I'm not aiming for simulation, maybe this is just getting tired of RTSs with the same formula. Maybe I should try Dawn of War...