At this point, the word "filler" doesn't mean much to me other than "something that doesn't move the plot forward". It might provide intrinsically useful character development, be seriously entertaining, flesh out sketchy moments -- but not move the plot forward.
Basically, I see it used so often to mean anything outside the skeletal milestone points in the plot I'm never really sure what the user actually means anymore and there's no consistency on whether it is meant as a pejorative or just anything outside of the bones.
For those reasons, I've basically stopped using the term.
I'm not sure Obelisk is "complaining" because "filler" isn't automatically a "complaint".