Look, all I know is that precious Dev-time was spent making this great dungeon. And for a little time loads of people were having fun here and enjoying this.
Then some Dev found out people were not doing last boss the intended way, and corrected an issue - resulting in total abandonment of the instance. The consensus is that the dungeon is broken/bugged/not doable.
Whatever you call it, why can't this fix be reverted for a period of time while you guys can reconstruct, test and deploy the proper way this last encounter should be done?