WoW didn't die from being made more casual, as from day 0 it was designed as a streamlined and more casual version of existing mmorpgs at the time. Some of its lightning-in-a-bottle success in the early days such as questing, was originally due to "a navigation error in which players would accidentally wander into higher level zones".

It was more negatively affected by the amount of grindy and timegated aspects put in it. That made even their own version of the Palace of the Dead known as Torghast be known as 'Choreghast'. People may bemoan PotD and find it boring, but its never been mandatory for your endgame raids and trials.

There was also of how the devs didn't seem to really care about listening to the players, especially for shadowlands when they said they were listening but stubbornly still thought certain things would go fine with the players despite their protests.

Or of how many temporary systems would get added/adjusted/removed to act as a sort of treadmill for players. Like can you imagine getting Blade's Justice for drk from Bozja during shadowbringers, and then that same relic you obtained can no longer be obtained when endwalker launched?