I agree those to would be albe to get all those hms but then all of there move would be a hm and you would not be albe to change them
Yeah, that's the point. You don't need to change them, you use those pokemon as HM slaves, that compress the moves you need to get anywhere
in the world into two pokemon, leaving the rest of your pokemon to train however you want, without worrying about needing the HM moves.
And besides, ever heard of the move deleter? If you wanted
to change them, you can, but as I said, there's no reason to.