You don't really need kraken stance, since bosses are no longer immune to everything. And CB seems to be working vs many of them, so I'd say wolf stance.
Ureh and vizjun (assuming you want charm, because for farming enemies, throw barb is ok) - you want tank. Bear + runemaster, sword for whirlwind, and block. And then whirlwind to boss, you are immortal.
You can use same build to complete bremmtown, just skip all the way to dragon, you can even kill them by stopping in the middle, and using sor, half of them map will die in few seconds, even with moderate damage dealt by your char. It will only be little tricky not to get killed by death spiral, kill dragon with stormblast or ancients hand. You can do all of these 3 uberes with that 1 respec to such build.
Xazax is really fairly easy, his main weapon is slow, so, if you have wolf stance and fast run speed, you can kill it by just running around and spamming fortress. You can hit him in melee with stormblast type of skill to accelerate the kill if you want, but it isnt must. You can park those adds in the corner if there is too many, thanks to your superior movement speed.
Use the same build to kill QT, you don't need any extra resists or items. Just run around spam fortress, try to run around him, pass through the room, so fortress keeps shooting, and you dodge the beam. It doesn't instakill you anymore, so there is even margin for error. 10min and hes dead, no need any special prep for this uebr.
When it comes to tanky heroics, like astrogha or unformed land summon boss, you do it as melee, but you need gear, ideally ancients hand, stack res pierce (which isn't that easy to get). Fire rune weapon is nice (-60 from single sword). Two of these you are at -120 fire just from weapon slots.
Can go with shield too, for block and ~40% deadly strike.
What also helps, is all the old stuff, 50% slow from gear. In addition to that you can use screaming eagle, which causes multiplicative slow effect to weapon slow, both sources applied = massive boss slow. You can either switch for it (few points in skill and nihs for duration), or if you dont like switching, because it can be not triggering randomly, which is really annoying, then runemaster, offhand sword (unlocks ww, which is must in many fights, such as astrogha), and main hand throwing axe, which you will still attack as melee with ancients hand, but at same time allows you to use screaming eagle. In older patch it was possible to throw screaming eagle with throwing axe as offhand (other throwing skills were dealing 0 damage, but screaming eagle debuff worked). Now it doesn't work, you need the throw axe in main hand slot.
Anyways for those heroic bosses, you need better gear, good damage, and res pierce. Earlier you try it, harder it will be. For example astrogha has fairly high hp, so to kill it smoothly you really need decent damage, otherwise it takes a while.
As for classic fortress build, that just runs around with fortress, its good for many really first charms, that you can't get otherwise. Also bosses like qt, xazax. Even stuff like startled witch, you spec as full vit tank, use eagle stance, and then run around, purify it, while spamming fortress (and slow from eagle + your item slow). It is pretty easy actually. You don't need any extra open wounds, fortress hits it so many times, amunt from charm is enough. Fights where you really want 100% OW are ones, where amount of hits delivered to boss is limited by the fight mechanics, such as Laz fight, there you can't keep hitting him with fortress or atmg, only your melee swings trigger it, so you want them to pop open wounds as often as possible.