I think it would be great if raids stayed somewhat challenging even after each expansion. It would be a good incentive to keep you subscribed and trying to raid.
I am not saying that it should stay on the same powerlevel but come on, if you have been killing the LK 25 Heroic back in the days when it was current raid, and got the reins of the Invincible, and now everyone is doing the boss 20 times with their alt every week like if it was a slot machine, it is pretty disheartening.
So I would recommend blizzard that raid bosses get tuned so you actually need to follow some mechanics and actually need to get 3 or 4 friends to bring them down no matter what expansion so all the effort people put on getting gear and doing the raid are worth something.
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