Well these are all keen points. I do have a counter. For all the Ghosts in Pokemon, they all seem to have a connection to a realm that allows their body to have the ability to be intangible. Intangibility is a trait shared by Ghosts. So maybe they can eat-sleep-drink and piss like any other Pokemon. Maybe they're only classified by Ghosts due to that property alone, and are still for the most part physical creatures.
Because of their ability to become intangible-they also have an energy that is ironically able to ensure that Normal and Fighting attacks go through-because they're attacks that don't come from an Element-or are based off a mystical origin.
That ...actually makes sense...Holy crap!
No serious, check it!
Ice, Fire, Electric, Water, Flying-Basic Elements.
Rock, Grass, Steel, Ground--All part of Earth. They all are mineralic-that's elemental
Bug, Poison-Deal with the erosion of life. Bug because it irritates, Poison cause it corrodes.
Dragon, Psychic, Dark--mystical realms where the elements of the natural world do not have natural counters.
Fighting is a more Focused form of Normal to me, so that's why Fighting Pokemon get hit by Ghost attacks. But since Normal is well normal--well they just cancel each other out.

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