stoneskin = 30% redux (maybe?)
aura = 20% redux
shield = 20% redux
0.7*0.8*0.8 (is roughly equal to) 0.5
Rager resist looks like about 50% to me. Certainly better than 30%.
Max dam redux for a non-rager warrior = perma dam redux for a rager.
Meaning you have to absoloutely bust your ass just to draw level with a single rager power for a couple of ticks (during which they can flee and wait out your prep timer) as a non-rager.
In any case most warriors will only have access to aura and shield in exceptional circumstances and stoneskin will usually come with major drawbacks and be more difficult/costly to use as certain races. Damage reduction in combat heavily favours the battlerager. This shouldn't be a debate.