First of all, your teams seems really slow, outside of Raichu and Talonflame, you will hit last most of the time. For Ghost types, for example, Trevenant will most likely die before taking a hit, even though it's ghost STAB may seem like a good option to counter those types. I may suggest swapping Trevenant for a Dark type, like Zoroark, Krookodile, or Alolan Muk. Alolan Muk may be slow, but it counters really well the Ghost, Fairy, Grass and Psychic types, thanks to its great bulk and respectable attack stat. Krookodile is just great at what it does, and Zoroark is crazy fast, and it can fool the AI with Illusion, although i think A-Muk is the best choice. Your team seems kinda weak to electric types, even though Tyrantrum has Earthquake. You can go for Krookodile, as i said, but you can also use a Flygon. It has a nice speed and attack stat, alongside Earthquake as a STAB, and Dragon Dance. Another thing you need is some form of Terrain setter, Primarina learns Misty Terrain, but you can also use Sylveon, a favorite of mine in my playtroughs. If you need a Grass type in replacement of Trevenant, try Roserade, since it has access to Technician boosted attacks (like Hidden Power), Toxic Spikes, and Weather Ball if you're using Politoed, and Grassy Terrain. And it wouldn't be a post of mine if i didn't talk about... Whimsicott!!! Tailwind is invaluable in this game, and Whimsicott has Prankster, which means it's status moves ALWAYS go first. Priority Nature Power and Sleep Powder are awesome, and even though it doesn't have a really good special attack, it can nab some KO'es against super effective targets.