The main problem with 11F is that mobs have high debuff resistance, it's not the only one though. First mob overdrive is either all party damage + 10% scorch or very nice 4x 5k random damage, second has equally nice true double-hit with fire debuff as normal overdrive and 6k nuke as rage overdrive (and rage overdrive is ridiculously long). This fight either requires some serious turtling with well tailored team or serious damage to finish this before things get ugly. In my opinion this fight is much harder than floor 10.