I suppose, given the option between watching that arc and, say, a post-Order Ahsoka arc, I'd probably choose the latter. But that's no reason to disregard this Rex/Artoo arc altogether. Each TCW story is made for a reason and always has at least some redeeming elements for varying crowds.
I coulda sworn that it was an actual expression in English.
If you think hard enough, the entire TCW show could be counted as "filler". Just saying.
No, it's not. Probably because it didn't really fit.