>>32511386Well, gen 6 was really rough for ubers. Xerneas, then P-Don reshaped everything around them.
Palkia is free switch-in fodder for Xerneas, which can loose you games, it's speed tier isn't what it used to be, and it's ability to be a wildcard check for things has been seriously hampered by the fact that it is wholly unable to do anything about the 2 big threats, or their major counters. It doesn't help that Primal Kyogre is that much more specially bulky, in the off chance that you need a Primal Kyogre checked and don't want to risk your P-Don.
Dialga fared slightly better, since support mons are harder to outsource, but it is still at best a Stealth Rock stooge who is utterly helpless against P-Don and Xerneas.
Plus, 150 base SpA just isn't a big deal anymore. The best use I have found for them is pairing up Palkia and Shedinja, since Palkia will lure out Xerneas, Xerneas will usually burn its herb on the "free" turn, and find itself walled by Shedinja.