Well I can understand Greivous is a wuss in Ep 3, but i can understand how that would of stem from a certain event. Why would Count Dooku even keep him around as the main general if hes such a wimp, he could of made him a front line fighter commander like the jedi, instead of the great general of the CIS. Also the Jedi would not view him as a huge threat as Dooku was.
How i viewed Greivous in Ep 3 is that he was badly damaged by Mace Windu in the miniseries when he captured Palpatine, If you remember that season 2 miniseries was suppose to be a small bridge to Ep 3. Hence why he fled Obi-Wan and Anakin on the bridge. As for his duel with Obi, I can see how he was a coward to fight him, but isn't typical for leaders to send there guards first before they get their hands dirty, But when his guards failed he didn't become such a coward to order the droids to shoot, he faced him in a saber duel, but when he lost his sabers he had to run, hes nothing without his sabers, especially when hes fighting against a force user still holding his.
Again I know its a kids show, but the huge problem is that that stuff is now cannon and destroying what was already canon. Like Quinlan Voss for example, in cannon hes facing his demons (so hes confused and moody) and is not in a sunny disposition as shown in the series,
I like the idea of star wars for kids, because thats how we all became such fans of the saga, but not at the expense of killing the lore that was made, especially giving Anakin command of the 501st Legion so early and that Rex himself said that we are clones not droids, we wont follow blind orders like the droids. Hence they wouldn't follow order 66 without real facts the Jedi are traitors. But in cannon they followed the order without objecting,
"..... did we have any doubts, any private traitorous plots? Perhaps but no one said a word. Not on the flight to Corucant, not when order 66 came down, and not when we marched into the Jedi Temple. Not a word." 501st Journal (Battlefront 2)