Bleach D20

[Prplcheez]

i note one problem with that: most arrancar's release is enough to stave off a shinigami's bankai at the least and surpass it at the most. Resurrección: Segunda Etapa is a very large step above that, so wouldnt it be better than bankai?

There's also the fact that by and large, Arrancar are far more powerful than Shinigami. I think it is seen as the same factor of increased power. As most Arrancar can hold of a Shinigami's shikai without breaking a sweat, the original release is like their version of shikai and generally buffs them up to a Shinigami's bankai level. The second release puts them farther above that.