He was meant to be the moustache twirling western villain. A coward that does some bad stuff and flees.
A good point. Though seriously, I'm not sure what to think....
Someone repeatedly watered down like that was most likely intended by Lucas to be like that originally...
Lucas and Filoni met almost weekly according to Filoni, in person or on Skype, to discuss episode plans, the way the series is heading, and Character developments... I don't think George would let him water down Grevious if it wasn't intended, however it's always so hard to tell.
In the movies there's obvious signs that he's meant to be a coward, he sent Magnaguards after Kenobi and Skywalker, then after Kenobi... Because he was afraid to face them.
Maybe he was meant to be like this, *shrug*
The EU changed him into a bloodthirsty, genocidal, homicidal vessel of pure awesomeness. Needless to say that I prefer that version.