@SomeoneStoleMyName: I can tell you right now that 2H tank works just fine even on Nightmare. I got Bull using a 2H weapon AI-Tanking by him self. No other warrior in the group to share the damage between. It's not as solid as using Shield Wall but extremely do-able. Hell I even have him not using potions on his own now cause he rarely needs em now.
Only issue really is I have him set up for AI, not for players. Players can do a MUCH better job but your priorities will be a bit different. I got him Block n Slash immediately and then started down the SnB line. if you intend to be the only tank on the team that's what your gonna need to do. You wanna half ranged dmg, and the 20% from the front. And, obviously, remove flank bonus dmg is gonna be a biggy as more then 2-3 enemies have a tendency to shuffle to your sides/behind you.
Issue with this from a player perspective? It's kinda boring having just Block n Slash + War Cry for the next 10 levels. By lvl 2 your looking at max Block n Slash (once your outa intro and respec) with War Cry for the taunting. Then you need 6 points in SnB for the pass That puts you at... lvl 8. Once you got that you need to hit up battlemaster to head towards Combat Roll. Key to this, get the passive on the left. It weakens enemies anytime you crit. Super easy to ger 20+ crit with crafting. That means your crits lowers enemies dmg before it ever gets to your passives/armor for more mitigation. You can take all manner or little to no dmg with that.
That or you know, use Solas for his 30% weakens. Setting Solas up as a barrier machine + maxing out his rift stuff? Best thing you can do for your tanks really. Or you know, play a mage and go Rift... I've done neither of these things, mind you. I'm playing a Necro, I have Vivienne in the party doing barriers with Varric. Bull is literally the only tank I got.
Anyway, point is, you can do it either with AI or without. If your gonna do it, Charging Bull is definitely a must have as well. Block n Slash, C-Roll, Charge, and weakn on crit with the SnB passives? Everything else is gravy at that point. Oh and %chance to cast Unbowed is amazing... not as reliable as +5 block on hit but you know what? You can do both. Currently my Bull is using 5% chance for Unbowed (which happens often) and 15% dmg taken turned into 10s regen. Turn that into 10% unbowed with 25% regen and... yeah. Or 5 guard + regen, or 5 guard + unbowed. Really any combination of that turns your tanks into gods.
-edit-
I got another playthrough where Bull will by my only 2H tank (again) but im gonna try to go for regen on both items. Apparently that stuff doesn't really stack (usually) unless there different tears? If that's the case I'll end up doing the 20% and 25%. Kinda curious what that'll do... 15% is pretty amazing as is either way.