Few things:
Provoke tied to ANY potency backfires. People will want to use for potency and there arent any competing uses for MP which brings me to:
I think you overlooked the MP resource. You have lots of ways to gain it. equilibrium(20%), Skull Sunder+Butchers (unspecified). Passive accumulation, (potentially any jobs party buffs like goad now) But only 1 spender that costs 20%, onslaught on a 30 sec CD and a 50 potency provoke (20 sec CD). I'm not seeing much point in MP on war when its only active use is onslaught and screwing up everything with provoke spam for damage.
Assuming you dont spam voke and just use onslaught (2/min), equal covers 1. Passive regen probably covers the other. People will ignore butchers 100% of the time the same way we avoid defiance for more fell cleaves. Except now we get defiance for just being smacked and can use both IB and FC simultaniously. Without the enmity on butchers, theres really no reason for it to exist as it would never be used without some seriously good things to do with MP that outweigh another FC. Wars will learn to get by using only the free IBs provided by taking damage and just spam eye/path for FC forever.
If anything this looks to be reinforcing the current play style of spam FC but now you get the bonus of tank stance, IB, and even more max HP from passive IB/SC gains from taking damage which results in a damage gain while tanking. Not sure if this was the goal, or if this is to design war as one of the 'MTs' in a MT/OT split role world.
Without any reason to use BB combo except to sacrifice damage for more defense (we know how that goes), Theres really no difference between tanking and not except you get occasional free IBs to use. It sounds like a have your cake and eat it too version of the current stance system, which, while effective, doesnt sound very appealing to me personally.