Well I guess it could be considered filler, but it would be filler that is more needed I guess. Things like "Where did the rebel logo come from" "How did the rebellion start" "What Jedi did Vader encounter during the purge". I mean these were things that shaped the 15+ years between episode 3 and 4. Rather then the few years between 2 and 3.
Sure the clone wars are a very important part of the SW story, but I think we seen enough of it in Episodes 2 and 3 to allow us to fill in the blanks. The bits of Greivous that we see are could because it sets him up for episode 3, but the rest just isn't needed. Especially the parts with Boba. I thought he was better silent, mysterious, and badass... rather then young, whiny, and conflicted.
Once again, JMO.