Meloetta
A Pokemon that has been an incredibly consistent Pokemon throughout all of gen 6 should be on the first 10 places at least. Meloetta sums that up perfectly, really good Pokemon being the best option for a psychic type in RU during XY due to being ghost immune, trait that allowed it to handle doublade and effectively check opposing psychic type Pokemon and being a fairly adaptable Pokemon, with sub calm mind, specs or colbur calm mind which is a set that gained traction during ORAS and helped pull off double psychic cores. It just has been great, only worse on a metagame where dugtrio was so dominant but that hindered so many other Pokemon as well anyways.
Tyrantrum was virtually non-existant in XY and only started becoming an actual threat mid ORAS, I dont think it really deserves to be on the list. Not even as a special mention (12th or 13th place if anything).