I think another thing to keep in mind, at least when it comes to the trash pulls, is that the trash in the dungeon just auto-attacks and uses a telegraphed cleave, line, or circle AoE with a cast bar. If they had little mechanics with them without changing how long they take to kill could make them much more enjoyable, and the mechanics dont have to be something difficult or complex.

Could be like 1 mob applies a "Healing Received Down" debuff, making the tank take way less healing, so you'd target it down first and then go back to AoEing, or another idea could be that the mobs explode at half hp and 0 hp, so you'd either want heavy mit on everyone, keep everyone topped off with healing or kill them one at a time... or just blowing everyone up anyways.