They do have wandering mobs, they just spawn rarely and not on all floors. If you kill them they say something funny or lore related in the text bubble.

But yeah, they never changed the formula much since the first deep dungeon, the base design remained the same.

I would have liked to see something like "eureka/bozja x deep dungeon" - put 100+ people on the map, all spawning in some random corner of the map, maybe it has 2-3 layers each floor (max 5-10 randomly generated). PvP could have been enabled on floor 2+ (if there is a unique skill set to these floors different from PvE set, or only PvP skill set with something like rezzes for healer added - whatever), or you team up with other groups against bigger bosses and form bigger parties. If you die your corpse becomes loot and you restart from 0.
Just imagining outside of the floors, PvE guilds are forming together to build alliances against PvP orientated guilds who are camping certain locations, like what else are even guilds for atm?
Mobs like in a few dungeons where you need to pull undead mobs into the sunlight so they start burning and losing mitigation buffs. Or pull mud mobs into the water so they lose their protective shell - same concept. Or kill mobs by the aoe of another bigger mob. Or using traps like in temple of quarn to spike mobs up and cut their HP in half each hit. Or place the mob under the falling rock or erupting geysirs so it takes extra damage. That are all gameplay mechanics I want to see in a RPG, I don't need another dance to evade aoe and spread/stack and hit the boss for 5min to kill it.

There are so many more ways to make it more interesting and appealing than - have a pomander, now kill this mob like you killed all other 10000 mobs before in the same exact way.