Blue crawler is balanced because we have toadfish.
Toadfish is an unupped midrange hitter, but when upped, it fills a very differen role, so blue crawler is there JUST to fill the role of a midranged hitter in the upped bracket.
If we only had one or the other it wouldn't be fair.
While this may be true in some sense, Zanzarino, though inactive, did agree that a true upgraded version of Toadfish and an unupgraded version of Pufferfish (therefore separating the cards) was something he wanted to do because of how each card would be useful in its opposite grade.
