"Damage taken" ceases to be a meaningful comparison whenever Defiance is involved, because you're then comparing eHP increases via mitigation to eHP increases via increasing actual HP - which is why, to do any meaningful comparison, you have to use "percentage of max HP" as your start point and end point.
Honestly though, the current design is just bad and makes any comparison contingent on unfair assumptions that don't reflect actual gameplay. The starting point I'd personally like to see is for Fell Cleave and Inner Beast to be separate skills available from either stance, and Rampart removed from role skills in favour of bringing back native Rampart/Shadowskin.
That doesn't leave things balanced but it at least gives you a start point.
