Maybe mightynine would have some insight but other than DeMarco spilling the beans or one of us getting a gig at Turner, I doubt we'll ever know.
Sadly, all my media experience is in radio, where there is no filler to worry about (although we do use PSAs for fill!).
But based on every answer Demarco's given about filler, I would guess that it's just not worth the headache of trying to carve out certain episodes and it would probably be something of a nightmare to keep track on for both ends - what if episode XXX is filler, but Funi sent the wrong tape and it airs anyway and you've skipped the two episodes before it? Wouldn't that be confusing for the viewers?
Also, his Ask has been kinda forthcoming about the changes. Obviously not enough to ruffle any feathers above him, but you can tell he's frustrated (i.e. he says moving One Piece behind GL was not his call, cutting back the block may be a plan to boost ratings but it's not HIS plan), but he's also looking at the positive side that the block is now mostly premieres, which is something they couldn't say when it first returned - i.e., the fat is trimmed.
I wonder if someone thinks that pushing OP later will help prop up the back-end of the block. Hope that people stay up for it!