I feel like the Burn was only "difficult" because of how hard things hit. The trash and final boss hit particularly hard when it first came out, now that the average ilevel of (most) people is higher things are dying faster and tanks are taking less damage. It doesn't seem so difficult anymore.

I guess the final boss can be considered difficult because of his dash mechanic that you can't see from most angles, but I hardly think that's enough to justify the whole dungeon as hard. Most final bosses in dungeons have a bit of a difficulty spike compared to the previous bosses. I think the Vault and Doma Castle are good examples of "difficult" dungeons as at least 2/3 of their bosses constantly keep you on your toes.