Agreeing with this. Exactly what I would have done. Metal Coat can actually be found at the bottom of Chargestone Cave, so it can be found long before the elite 4. Having said that, I should say that I did almost put it in Low because of its rarity and its lack of speed as a Steelix (I didn't find its low Attack as an Onix to be that big of a deal), but I figured that since its Steel typing pretty much provides an autowin against a large number of gym leader/elite 4 pokemon (and unlike Skarmory, Steelix can actually be an offensive pokemon), Mid could be justified. I'm not changing my placement for Onix yet. I'd rather see what others think from testing it. If other people think it should be Low I'll change it.