are there any RTS games where you take control of only one aspect

>>384356059
No.

Some old ones have a mode where two people control the same faction but it's not really worth it.

World in Conflict would be the closest with how the game stresses teamwork between people, but I doubt many still play that game.

I must confess I haven't played any such game myself, but to my understanding it's not unheard of in board wargaming (and presumably some computerized versions of those games). For example, while The Campaign for North Africa is a meme (detailed to the point of being virtually unplayable), I know it is supposed to be played in teams of five with commander-in-chief and four subordinate commanders.

Of course, we're talking about strategic-operational games here so no economics, diplomacy or tactics here, but the sort of mechanic you're talking about exists at least in CNA.