The Arrancar Saga was murdered by pacing. It's one of those anime/manga arcs that flows MUCH BETTER in a binge watch/read session or three. It's not that the actual plotting gets better or anything, but not having to wait a week for another chapter or episode and having the option to omit filler episodes/arcs makes for the intended uninterrupted pacing.
Bleach had the same problem with filler that most of the big three (of any era) had/have. Plotlines that take up like a third of the total runtime of the story that are TIGHTLY locked into their own timeline. This means that when filler has to appear, it has to be either set in the narrative's past or in some magical AU where the characters have the same knowledge and skills as the current Arc, despite there being no feasible way that the location and timing would match up.
That said, narratively the Arrancar arc's first instigating action is the capture of Orihime, which Halfway through the Arc is revealed to be a big troll from Aizen, essentially, which serves to make the audience feel like fools who wasted their time on a Canon filler arc. Then there was a tease for Orihime's power and character development, implying she would become a mover for the plot. She still develops a bit, but the lion's share of her character growth is shown in the Fullbringer arc, as opposed to the story where she's the primary goal of both the good and bad side.
Like...there's really compelling MOMENTS in that arc. It's like someone threw a jigsaw puzzle made of gold onto the floor and refused to let you solve it. Really good components haphazardly arranged so that their good or even great individual parts lose their beauty and cohesion.