And from what I understood they only had concept art for Grievous to go off of, so they had to invent his personality on their own.
But to be fair, I understand why George wanted to make this General character a mustache-twirling villain that runs away and gets beat over and over. It fits into that villain archetype of old serials. I don’t think people would have been as disappointed if Grievous had just been set up that way in the micro-series as well.
Growing up I always rationalized the characterization difference as Grievous being pretty powerful right after his transformation, but slowly became weaker as his remaining organics struggled to exist within his cyborg body.
Only the serials I’ve seen have better villains. Grevious doesn’t hold a candle to Ming the Merciless!