Randomizing the trash mobs will not really change how a dungeon plays out. How much does Halatali NM change when you get bombs versus getting lightning sprites versus getting chests after pulling a chain?

The following mobs are pretty much the only ones that change how trash fights go:

Summoners (Manor Claviger in Haukke HM, Illuminati Footman)
Crowd Controllers with hard to dodge aoe that inflict Stone/Terror/Sleep (Manor Claviger)
Bombs