[Coda]

They stopped caring about the National Dex after 4th gen. It seemed fairly explicit when Black and White had no past Pokemon at all and the only way to get them was to do a cross-generation trade.

No, trash Pokemon exist to give them the opportunity to fill up the world with a bigger variety of creatures. The series has always been vulnerable to the strategy of "aggressively level up your starter". If EVERY Pokemon was good, that would get worse -- players would just stick with the first few Pokemon they caught and basically never switch unless there was a significant type disadvantage that needed to be overcome. And if players are going to do THAT, what's the point of spending the design effort making more?