I know some people might argue about his performance in EP III. But his chest was choked by Windu. Also even Windu said Obi Wan would have the best chance against him in the novel. More importantly, in EP III we already got the death of Dooku, the downfall of Anakin and his duel against Obi Wan, the reveal of Sidious and Order 66, GG is just a small part of it. But in The Clone Wars, no matter how cool Maul, the Dathomir Witches or Mortis are, the major conflict, the most important war is between the Republic and CIS. Since Sidious mostly has to stay behind the stage, Dooku and GG are the most important leaders of CIS, surely they should be portrayed as powerful and threatening villains to let the war become more exciting to watch, Dooku would mostly make the schemes, GG has to be the Jedi Killer. Not something like let Dooku get owned by pirates or witches, and surely not something like TCW GG.