Ackshually
End game is still the main focus on all expacs, the difference though is that end game is not the only place you get gear upgrades, at least it was not for me.
I would run MC and if I was down on numbers I would go back to lower dungeons during the week and on weekends before the raid and get some more gear. Because back than doing some lower dungeons could still give you a piece of gear that would actually help rather than whatever the next iLVL is.
Best example would that Onyxia and Rag were released with the game, Rag being the big one and needing specific items and classes, for example Frost Mages and fire resistance gear.
BWL was next which you could still use FR gear and follows by ZG, that did not need FR gear, so you had to change it up, although it was not exactly on the same scale, by than they were changing it from exclusively 40 man, you could technically just get the best gear you could find to finish it.
But than came AQ, which had both a 20 man and 40 man respectively, again same as ZG, Ruins of AQ could be beaten with whatever gear, but in the 40 man, much like MC, you needed specific gear, so instead of just farming AQ20, ZQ or BWL, some people were going back again even further, going back to 5 man dungeons to farm specific nature resistance gear.
Than Naxx came out and your NR gear was pointless again, so you had to once more go back to dungeons, get the best gear you could find along with what raid gear you had and start the journey all over.
But than BC hit and it was a roller coaster ride downhill from there. Looking at the WoW timeline of when things were released and cleared it became very evident that the whole farm gear to clear the next raid was becoming redundant. Raids being cleared weeks, days or even in rare cases the same day it was released.
Move to today’s standards and if the raid is not cleared on the same day on normal there is probably something wrong with the raid, and that is with nothing more than the gear you got from the previous raid.
Hands down I can bet my house if I owned one, Method or Limit will clear The Crucible of Storms within hours of it’s release and possibly on the same day Siege of Zuldazar at least on normal.
If they release the raids the same they done here, as long as RNG is good they will clear each heroic within a week and much like current the moment their iLVL is high enough, Mythic also.
There is no going back to old raids, the iLVL of everything current is being upped to allow players to farm the same stuff we are farming now but simply progress the new raid rather than the old one, there is no need to go back anymore.