Palkia

Palkia's CP is too high to enter the Great League

Palkia has virtually no use in the Ultra League due to its restricted CP and lack of solid niches.

Unfortunately, base Palkia is strictly outclassed by its own Origin Forme.

Base form Palkia was once a solid choice for the Master League, and in Season 17 - Timeless Travels, it became an excellent response to the rise of Fire-, Ground-, and Ice-type Pokemon and attacks that resulted from the season's buffs. Kyogre also became indirectly prominent, and Palkia stopped that in its tracks. Palkia's longer history in the Master League had its series of ups and downs - competition for a team slot against other Dragon-type choices were fierce, and its Water subtyping defined whether it would be in the meta or not. At times, it found itself struggling when Rayquaza or Dragonite were prominent, and competing with Zygarde for a teamslot was also challenging. But from time to time, it gained clearly defined niches, and it became a strong metagame threat whenever it happened.

At the peak of Palkia's viability, it was suddenly knocked off its course when its own Origin Forme was released. Palkia-O has strictly superior stats, access to the same attacks, as well as a more reliable Dragon-type attack in Spacial Rend that Palkia craved for so long. Palkia instantly went from hero to zero, and there is now absolutely no reason to use it if you want to win. Palkia now awaits for a move update to become somewhat relevant again, but since its base moveset is already quite strong, there isn't too much Niantic can add to make it good again. Perhaps something like Breaking Swipe can make it worth running again.

Palkia now finds its home in niche, unofficial formats such as Draft or a point-based teambuilding format. Casting its Origin Forme aside, Palkia is still a strong Pokemon and demands respect. But in any format when either Forme can be used without a higher cost for one, Palkia-O is superior in literally every single competitive metric.