As much as I like using characters like Lizardman, Nightmare, etc, I also appreciate their distinctness within the roster. One thing I liked about Soul Calibur is that the world--for a time--seemed to be somewhat ordinary outside of Soul Edge's influence. Sure you had an unusually active Greek pantheon, mystical figures from ancient times, and the occasional Jell-o Fury, but these were kind of hidden to the outside world.
It's one of the things I didn't dig about SCV. The world had become much more openly fantastical with the whole malfested business, and stages where giant monsters are flying around willy-nilly, and characters like ZWEI and Viola just show up with completely new forms of magic whose sources are unexplained. It started looking more like Lord of the Rings.
When everything is fantastical, the fantastical characters and occurrences themselves feel a little less special.
I still want Olcadan to come back though. If boring ol' Edge Master can be in two (maybe three) games, then owlguy should get another shot too.