Gilneas, I can't argue that it's not a progression. It isn't. It very isn't. It's a regression. I just wish it was a progression.
Compare the progression, as you have laid it out, within each expansion:
Tamers -> Pandaren Tamers -> Spirit Tamers -> Beasts of Fable -> Celestial Tournament
Menagerie -> Fel Pets
WQ's -> This
Getting shorter all the time.
Mists of Pandaria still has the most interesting challenges. Since we have developed, and since filling a roster is so much faster and easier now, I'd like even further progression, but as it is, I'd be happy if we just had as much challenge and progression as we had back in Mists.
The Celestial Tournament remains the pinnacle of battling.
I don't have a problem with the idea that someone who starts it the day 7.2 comes out should feel that getting to it is an achievable goal. However, all of PvE pet battling, apart from Family Familiar and Awfully Big Adventure, can be done with about 30 pets. Maybe add three or four specifically for PvP, and you're done, apart from the collecting aspect. The way Blizzard are raining pet charms and stones down on us in Legion, 30 pets is pretty trivial now. They don't even have to be levelled - nearly all can just be bought.
Good News, Everybody!
Cymre has brought us the first video of the Pet Battle Dungeon.
It is as Quintessence has described, but this is a full run.
Bad Stuff is happening in Wailing Caverns.
Go through Wailing Caverns, clear the trash (= wild battles with White-quality pets), and defeat the bosses (solo Purple, or Green or Blue + back-up), and finally the end-boss (Orange Elemental with no back-up team). You are allowed to heal.
That gets you a Purple stone.
This is obviously a very very easy challenge, and apparently it's weekly? Cymre just strolled through with one team of [pet]Lil' Bling[/pet], [pet]Amber Moth[/pet], [pet]Iron Starlette[/pet], without changing anything until the very end, when it would obviously not have been a great idea to take on an Elemental with two Mechs.
Now you get a follow up quest to do it again, this time without healing or reviving. Even without healing, it's going to be very easy for anyone with a CT-capable roster. It seems harmless enough, but there's a line in the quest text about getting the Damp Supplies "if you can beat my best run", which sounds like a timed run - truly horrible. NOOOOOOOOOOO, please NO! I know I joked about having M+20, but I meant difficulty, not the destruction of enjoyment that is rushing. We'll just have to see if they follow through with the threat.
Major props to Cymre for getting a full video out quickly!