Blizzard recently nerfed a bunch of things in normal mode Hellfire Citadel, the last raid of the current WOW xpac. The previous model had been that Raid Finder mode was ridiculously easy and had many mechanics removed, normal and heroic mode were identical except for the numbers, and mythic mode was much more difficult both in terms of numbers and mechanics. This xpac I never took part in mythic difficulty so I can't speak authoritatively on that point, but from everything I have read the mythic raiders were very impressed.
Throughout the xpac it felt weird to do normal and then heroic with no changes in strategy. Aside from 'have better gear' and 'play tighter' there wasn't anything else to add. It always felt a bit strange to have nothing more to learn, and honestly made heroic feel like a bit of a letdown. I was always a lot less interested in heroic modes in Highmaul and Foundry and after seeing Hellfire Citadel through on normal I just had no interest left in pursuing heroic.
No however Blizzard has removed a bunch of mechanics, especially on the harder encounters, and I am sure people stuck on those encounters will rush through them now. They defended the decision to remove mechanics entirely instead of simply nerfing damage by saying that it was silly to list mechanics that did so little there was no reason to pay attention to them. Focus on a few things, make those things actually dangerous, and pull the rest out entirely. I agree with that strategy completely.
I suspect I would have enjoyed raiding more this xpac if the entire thing had been done this way. We would have proceeded more rapidly through normal mode for sure and the heroic modes would have felt interesting as new things would need to be incorporated into our strategy. The fights always felt like a huge amount of information was incoming at the beginning and then to have nothing new arrive the second time around felt - off. Certainly the numbers still have to go up, and the general tuning can be tougher, but adding a completely new thing to deal with would keep me interested I think, moreso than the old design.
In general going through the same content over and over again is going to have limited appeal. Running the raid on Raid Finder, then normal, then heroic is a chore and burns it out quickly. however, I really do think that ratcheting up both the complexity and the tuning for every difficulty setting is the right way to go.
Here's hoping they do this for the next xpac, whenever that is.