I probably should be doing more silver challenges come to think of it
I still feel like doubledoom is meant to be "baby's first hard dungeon" (and I mean that not at all negatively) And even if you did grind more before going after hard dungeons than I did, I suspect that you unlocked the hard dungeons in the four (or at least 2 or 3 of them) directions before doubledoom.
IDK, later when I have done lots and lots with this game I think doubledoom will always be a fun dungeon to go to because of the completely random bosses, and at current it is a good level of challenge. I'm pretty sure I will beat it 90% of the time, but I have to engage and think to do so, and I often find myself enjoying that kind of challenge. For me it just seemed to unlock at a very strange time :/
For me it unlocks along with the likes of Ick Swamp which seems very difficult indeed, and Rock Garden (which has 3 bosses 2 of them with opposing resistances)