And yet there is evidence to contradict the show.
The CW is a very poor thing to use for any Vs. thread, because of how overpowered they are. If Lucas had made it himself, it probably would not be so overpowered.
Grievous was, possibly, never as good as he appears in the show. He loses to Kenobi in under a minute in ROTS, whereas the television show shows him killing people better than Kenobi with ease. Meanwhile, everywhere else, Grievous runs when there are too many Jedi fighting him at once.
CW is not reliable.