Actually Cata showed just that which is why MoP returned with so much grinds because Cata was too casual in terms of grinds and weekly time commitment. It was fine if you only played a handful of hours a week then content would have lasted you months, but for the "casuals" that played more than that the content lasted a month if that. The leveling grind in Cata was even shorter and players made far more alts earlier in the expansion to counter the lack of grinds than players did in early WotLK. MoP showed that the player base isnt as casual as players think. All the dailies at once might have been a bit too much, but there was "casuals" who loved it.
If you look at WotLK grind for five man players that didnt raid they had to do a daily heroic every day of the week while earning a fraction of the badges that a raider did which on a gearing grind standpoint took five man players about four times as long to exhaust the badge vendor. Cata on the other hand by response of non-raiders increased the reward rate which reduced the grind which left a predictable time point for players to complain about not enough gear on the vendor just a few months into a tier.
Cata struggled more from lack of content on top of accelerated content consumption rate due to faster grinds which then lead to players butting up against other forms of content to keep them busy. I only played a handful of hours a week though so I didnt get bored unlike the no-lifers that call themselves casuals.