Flashbacks are generally good when you read at one go...also, this fb showing the scabbards and their development/Orochi character also...it is not just Oden fb...I am expecting 10-15 chapters of flashback and I think "tragedy" part of ACT 3 covered by flashback...and act 4 starts with raid, Neko and Marco entrance, probable appearance of some warlords, Jimbei and Germa etc.
People who don't like flashbacks should seriously take some break from OP as lamenting over them not gonna help anyways...