70% or 90%, I don't care as long as most good deck concepts fitting for that group can get that high. The point is to have much more decks that can get a good win rate because the current situation, rainbow has 60%+ everything else 30-50 or even less, is bad.
And yes, "most challenging opponent = best farming source" is also bad. Those two should be separated. Making Half Bloods play with 100 life and all upgraded cards would solve that problem. False Gods should instead give other rewards that make them worth playing, like a free nymph or other rare for every time you defeated all 24, but they shouldn't be the main source for normal upgraded cards.