The current system in 4.0 is about that you have to decide which of the three units are needed most.
But you basically want to get all three types just 3 times, so the system is gone and strategic perspective is gone.
It looks like unified Minas Morgul and Dol Guldur into the one building ... for instance.
There it is about tactic with Erkebrand.
"Erkenbrand (the most expensive) can temporary summon two more battallions of the units you chose for him to lead."