OT happens because ECR demand trains in a certain sequence.
In case of GZB you may have observed 02581 and magadh are made to wait in Maripat or somewhere else, Because NR demands train in certain sequence.
NCR isn't insane in matters of controlling nor it has any hate for Duranto, Demand of Next zone is considered in controlling.
Mahabodhi and VS are...
more... given precedence because they don't slack ahead, but ECR manages duranto well in DDU-PNBE section and utilises slack.
What RB should do is amend TT of DURANTO and 04040 to depart from Delhi Behind VS and remove slack in ECR.