But you have also to think about something different:
Other factions have extremely powerful hero units. Other factions have a unit which is multiple times stronger. Mordor's strength is more the powerful spam - therefore we gave them a unit which costs no cp (therefore no spam), but is a bit less powerful than hero units.
If the unit would be weak, they would just be another unit, but not as impactful as a hero unit.
So just look at them in a different way:
Other factions use some CP to get a really strong unit which kills everything.
Mordor uses normal orcs and Cirith Ungol Orcs to kill everything.
If the units wouldn't be powerful, they wouldn't be (together with some more orcs) as powerful as elite units.