The mortar is 400mp thus limiting unit build early game, I just use scout car harassment. The only way to deal with them at the moment is to kite and flank it, the unit is OP on certain maps.
-Again, being expensive does not justify over-performance. By the same logic we can say Obers are 400, why nerf them? Or Ostheer's panther is very very expensive (considering teching) so it should have Blitz-thethefuck-out of every combat situation. Or we can say Stuka CAS (Lightning War) is perfectly fine since it's 200 muni. But these are all examples of units (and abilities) which are over-performing despite being expensive. If the mortar is to be nerfed, they should definitely lower its cost.
-In smaller games (1s and 2s) you can't simply "kite and flank it". It has 6 men and can retreat with only one, and in some very small maps (Langres for instance) it cover half of the map when positioned inside the base so going for enemy's cut-off is out of the table.
-Most people use 120 with Guards, good luck harassing it with SC.