Erm... correct me if I'm wrong, but wasn't it implied that his "rehabilitation" was solely due to some bigshot lawyer throwing money at Arkham until they agreed to rewrite Riddler from "sociopath" to "eccentric", rather than any genuine competence on Arkham's part?

Go over reformed!Riddler's (admittedly short) career again - I don't think there's a single instance of Eddie displaying empathy for anyone. He's still a sociopathic jerkass who would probably smother a baby off if it would save his life - he just plays by "the rules" now.