>>34881465I think that pokemon types are more of a layman's view of things where they're not so much concered about what a creature actually is but what it does in a fight. If some kind of giant bird and a sloth both breathe fire in a fight and thus hate getting wet, I'm not going to be worrying about scale patterns and phylogeny.
Basically, types are a generalized way of looking at a given monster's strengths and weaknesses without worrying about silly things like genetics or natural history.