I think there is a slight diff between Editoral Mandate and what happened in JLA...
JLA is one DC's Big Gun Titles as such everybody onboard that title needs to be kept in the loop on whats going on so the book stays consistant and up to date with the rest of the Universe and not too jarring for the readers, as such having to re-do parts due to the latest greatest crossover shouldn't be a shock.
However...
- A Writer shouldn't find out about Mandated Cast Changes from Fan word of mouth or the internet before he hears it from his editor
- A Writer shouldn't be told one thing...then have that decision reversed months later when the book is ready to PRINT and beign forced to re-do scenes...Note the scene in JLA that was SUPPOST to be about Roy's Mouring Kendra's Death...he had to change the dialog...but the ART HAD ALREADY BEEN COMPLETED, they didn't even try to photoshop the gravestones out of the scene...ugh
Those are things that can be blamed on a publisher...and not the writer and shows whats really wrong at DC...