That dungeons is entirely level based, I did it at level 30+ in my first playthrough and it contained deathlords, I just went through it at level 4 now and there are no deathlords at all and the highest level enemy was a Draugr Scourge (he was the "boss")
I got there at level 11 and it contained plenty Deathlords. Level 4? That's pretty low. I don't know how you did it. It gets too easy at level 30 because Deathlords stop using disarm spell.
Okay. I just created a new character to test this. I'm on a PC and got the game on Steam, and I'm on version 1.5.26.0.5, and the difficulty is set to Expert. This time I went directly to Whiterun and went to Jorrvaskr. My first (radiant) mission for the Companions was to clear out the Forsworn at Serpent's Bluff Redoubt. I played through 6 times or so and twice it was some fist fight at the inn, and the rest were at Serpent's Bluff Redoubt. So I go there at level 1 and when I clear it out, I'm level 5 and half. I fast travel back to Whiterun and get the Proving Honor mission and when Farkas and I went in to Dustman's Cairn, I was still Level 5.
Everything seems pretty normal going through the dungeon and by the time Farkas and I arrive at the boss fight, I'm level 8 and half.
I the first Draugr that pops out of the coffin is a Draugr Deathlord. I have been paying attention to Dustman's Cairn because facing lots of Draugr Deathlord seemed unusually hard at level 15 or 20, let alone level 8.
Does anybody know when the dungeon level gets determined? Is it your level when you enter the dungeon? Or is it your level when you reach the final cell of the dungeon? Or maybe it's your level when you are told to go to a particular dungeon?