At the danger of getting torn apart... But..... to me (and I have lots of guild mates and friends in the game sharing that opinion).....
The Timeless Isle is the worst event Blizzard has ever put into the game. Collect 50 Stones, Kill 20 Elites, Kill 5 rares....
Let's start with the 5 rares.... That is doable, rather decent. One cannot expect to find 5 rares sitting side by side to kill them all within a couple minutes. That quest is okay...
Kill 20 Elites, that quest is a little more tricky, and takes more time than the rares, and it does (depending on realm population) cross the line of ridiculous grind for just a bit.
But then the 50 stones, that quest is outright idiotic. It's a weekly quest one could say. Don't have to do it all at once. Well, the supply quest in Barrens was a weekly quest too, and yet still, one could have done that quest in not more than 30 - 45 minutes. And that, with complete neglecting mindless farming/grinding mobs.
On top of it, the totally out of line spam from stupid addons in the zone chat.
Isle of Thunder, and Barrens had a reason for addons. There they were helpful for the community, because the targets ramped up their health, the more people hit them.
The Timeless mobs don't ramp up. No one gives a shit if a turtle just spawned or died. Those in the proximity of the turtle see it. Those not, won't make it there anyway.
And that is valid for all rares. So, if you need an addon, because you cannot remember where the spawn points are, then for the love of god, turn the damn broadcast feature off. It's annoying. And if you don't have one, but rather constantly have to ask where and who spawns, get a damn addon, and too make sure it won't broadcast.
For myself, I go to the isle for only one reason, and that's to kill the world bosses there. Once they are killed, I'm happily leave the isle again. The Valor I can get there I get much faster through other means. The gear that drops there is horrible itemized, which means I get better gear through other means as well.
Anything else one can get there, is basically just pets, for which it's more productive for me to simply buy them, and make the money back in other regions that are rather abandoned. And a mount... Whether I get that in 2 days, or 2 years is to me rather irrelevant. Achievements are there too.. I get them too, once the isle is rather empty again, and I don't have to basically sit there and farm the rares until they spawn. Only costs time and productivity I can put to better use through other means.
So in a way.. The OP is actually correct. Considering the HUGE time sink, the isle is worse for gearing up than running dungeons. Whether dungeons are more intelligent, that remains to be questioned. They too are pretty mind numbing... lol