And there’s also the fact that they’ve retroactively buffed/reworked bosses in the middle of a raid tier exactly twice and both times they did it, the results were disastrous.
Case in point: Kel’thuzad in SoD, and especially Zskarn in this raid.
They will not buff bosses midway into a raid tier again. I think they’ve heard loud and clear that doing so on Zskarn was a catastrophic mistake.