Timeless was miles better than Tanaan.
Timeless Isle and Tanaan both represented the single final outdoor activity for a nearly year long drought, you can't look at them 'in a bubble' and ignore that. timeless isle literally had shit to do that would take you the rest of the expansion at a casual rate, and it had people DOING that stuff the entire time because of it. It created its own little ecosystem and it was entertaining.
You say hte pvp was a chore. Why? It was pretty awesome 90% of the time. You absolutely did not 'need' any buff to do anything on timeless, they were just convenient. Similarly, the slower rare spawn rate directly led to a better community feeling there - a good rare would spawn and everyone would flock to it, you could actually count on seeing the regulars any time something cool was coming up. Along those lines, the rewards there actually felt cool and meaningful, instead of a bunch of random 100% drop shit that everyone had after the first day which then became worthless. You could get a cool pet drop like the Ruby Droplet and go "Oh nice!" and keep it and feel cool, or trade it, or sell it on the AH. You had awesome items like the fucking falling star that let you rocket around the world as a meteor. You had reasonable little minigames like the crane falling coin collection and the trivia daily game. The different areas of the zone served distinct purposes and had tiers of difficulty, instead of just a mishmash of 'here's the fel orc part' and 'here's where the beasts are' but they all feel exactly the same.
Tanaan might as well have been exhausted of content the first day for how meaningful any of it felt. It took all of the goodwill they earned with timeless isle and squandered it by losing the plot of what was actually fun about timeless isle. You're right, you couldn't finish Timeless in a week. Good thing we didn't have a week of the expansion left.
Also it seems ridiculous to bitch about the pet battle part, that shit was beyond optional, as far as pet battle content goes it was the best in the game at that point, and it's certainly not relevant to how cool the isle itself is.
Summation: The Timeless Isle is actually the single best piece of outdoor repeatable content they've ever made in wow. Still. I can't even imagine how many hours I spent there, and I STILL need a crab pet to drop before I'm done.