>>57225854Psychic has gotten worse in every Gen since Gen 4 while all of its weaknesses and competitors have only gotten better. It was bad enough when moves like U-Turn and Sucker Punch got introduced but the Type chart changes in Gen 6 nerfed it even harder than Dragon. Steel losing its resistance to Ghost and Dark made those types much harder to check and Fairy practically makes Psychic obsolete, it beats Fighting AND Dark with a much safer defensive profile. Poison becoming more prominent to counter Fairy hardly helps Psychic because 9 times out of 10 you'd rather run Ground to hit Poison, Steel and other types. Gen 6 also though it would be funny to make Knock Off five times more powerful, so it goes from a niche utility move to Dark-type Earthquake that you can slap onto anything.
Gen 7 introduced Psychic Terrain and Tapu Lele to set it, which helped stabilize Psychic a bit by blocking priority moves (Sucker Punch) and boosting Psychic moves, especially Expanding Force introduced in Gen 8, but the Tapus aren't in Gen 9 so this is much less viable outside of doubles.
Mew has the same role it's always had, learning a shitload of moves that give it a shitload of options, mainly giving your team utility. It has fluctuated between OU and UU since Gen 5.
In Gen 9, Mew has more options than ever with over 200 TMs in the game, but as a casualty of Game Freak's efforts to curtail the distribution of many powerful utility moves, it has lost access to all of its significant healing options (Roost/Soft-Boiled) and Defog, which significantly limits the roles it can play. Its main current niche is a hazard setter on offense teams in UU. There are a variety of more specialized hazard setters in OU and beyond, like Glimmora's auto-Toxic Spikes, Hisuian Samurott's unblockable Spikes, and threatening Sticky Web users like Ribombee and Araquanid.
