>>42848651It's not always just having a x4 weakness, as there are many success stories there, even beyond what you mentioned (Heatran, Scizor, Ferrothorn, etc.), but also what the x4 weakness is. It being Rock really pees in Articuno's cereal, because it's not just about incoming attacks, but SR, as well. Having to waste your only item slot just to account for that is still a detriment.
And even that aside, we're talking about a beast with other prominent weaknesses, such as Electric and Fire, which are regularly carried for coverage purposes. It also has few notable resistances, and its immunity to Ground is relatively trivial, since most things which run Ground moves also compliment them with Rock coverage. Bug is a resistance that will seldom be useful.
The stat distribution also doesn't help it. Ice is just too defensively horrible a type to try and be defensive. If those triple digits were swapped around to Sp. Atk and Spe, it'd fair much better.
And, lastly, is its barren movepool. It really just doesn't have any noteworthy tools in its arsenal. It pretty much just gets generic Ice moves and generic Flying moves, whereas most legendaries have pretty wild movepools, incorporating things a normal Pokémon of that type and style would never get (think Ho-Oh getting Thunderbolt and Giga Drain, for example).
