Umm... I would say Magnezone. I mean, yeah Magnet Pull great! But when you run HP (Fire)/Volt Switch/Thunderbolt/Flash Cannon, you wall dragons, but dragons wall you! Considering Latios carry HP (Fire), Hydreigon has Fire Blast/Flamethrower, Magnezone definitely sucks at walling dragons. I mean, it's main role isn't walling dragons, but rather a steel-killer, right? But oh wait! Silly me! Scizor often run EVs in Sp.Def and carry Superpower! Heatran has Earth Power and Magnezone can't touch it at all except Thunderbolt, which Heatran walls pretty well, lke the Sp.Def variant. The only steel it can take down is Ferrothorn and Forretress, but the latter carries Volt Switch *buzz*. And when you run into a rare Bulldoze-Ferrothorn, yeah.