[Deathblob]

Well, the Hannya does have the demon and cold-blooded traits, which can be disadvantages (End of Culture and End of Weakness are not nice to Hannyas.

in M1:
Sorc = 115G/6R = 19, Hannya = 200G/8R = 25
in D2:
Sorc = 115G/4R = 28, Hannya = 200G/6R = 33

So sorcs are always cheaper researchers.

In addition, they have totally different paths. You're not going to cast many army buffs (or debuffs) with a Hannya. Hannya are really only better at battlefield evo (unless you are up to RoS, only a Dai Oni or a EA sorc with boots can do that), and maybe making undead archers. Yomi has great thugs, there's not much point in using Hannya as thug mages, any item you make is better off on a Shura or Dai Oni.