Considering the Respite is around the size of an aircraft carrier that is another whole ball game. Honestly SOME PokeDex entries make a Pokemon too powerful (and also make no sense), and that one is definitely one of them. I mean if a jet running into a Metang will not leave a scratch then how can a Fighting Pokemon even hurt one with punches and kicks? Or a bug type harm one?
I understand your train of thought and yes it matches the flawed Pokedex entries (flawed IMHO), but that would basically make him immune to almost ANYTHING physical which a Metang is not (resistance to Fighting/Bug types is 1x... If crashing a Jet into one does nothing then how can that little bug do damage to one?). I have no problem with you being extremely tough (as you should be as a Steel type), but there has to be a limit somewhere.