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Having 150+ new Pokémon again means that the quality of the designs will be lower than usual since Game Freak will be less strict because they want quantity over quality.
Look at Gen V for example, most of the Pokémon didn't even look like Pokémon at all, most of them had a "Fakemon feel", BW feelt like a game made by fans like Uranium or Sage.
That's the thing having 150+ new Pokémon would mean 70% of the new Pokémon will look like Fakemon,Yokai, Spectrobes, Temtems or Bulu Monsters, basically they will look like if a rip off dev made 'em.
Do you really want a Generation were all pokemon look like that?