I know the weapon well, @Zeatros , but not even a fitted Musashi will come close to the performance of a legendary hammer in this scenario. 2 HA with the Gada and they are dust, in a Agi build.
But if you want some power, drop the stamina stuff and go for strenght and agility. 10 vitality for that dungeon is more than enough. You can put the rest in gritt. If you really struggle and need steel thewed, go half way in agi or strenght. It’s not like you’ll find hard fights there and with that build you won’t survive long against a player who isn’t built on encumbrance, so…

Ps- Just pay attention because the hammers will get you into negative stamina if you push it, in this new system. It won’t regen instantly and you can take punishment if you screw up. Other than that, there’s nothing to worry about.