for me both are clear game changer and defense booster. if you don't have em you have a hard time competing with the rest.
so i think it's out of line when those lucky guys who have the 3 premium chars (vhe/wrath/astra) in game have such a big advantage over the rest. ofc there should be better toons who should help you with your defense but:
if you compare a normal 15% defense with a premium 38% valk defnese this an extremly big deal. most of this boost are due to one valkyrie which makes her too strong. wrath defenses don't have such a huge advantage (as long as you don't pair two of them --> hi nicko )...
look at the powermove of the valk, permadeath and healblock for 5 power along with buff removal and stunning for a basic attack and a nice passive too for a 4* hentai chick?
i would take her over wrath every time although he is clearly better for farming PVE (but who cares for that).