What are you talking about? All we saw was Orochimaru and Sasuke visiting some forgotten, inconsequential island. And a few Anko flashbacks. If Kishimoto ever intended to tell more about Anko's past, then you might be right. However, it's not like Anko is any central character in the series like Kakashi, for example. This might very well have been the most prominent history of Anko we were (not) ever supposed to get.

And I didn't see any particular Orochimaru character development. He was the same old Oro: Manipulating and laughing at people, and not caring for anybody but himself.

This filler arc certainly didn't do anything to change the fact fillers have zero impact on the main storyline, in my opinion.