Mamoswine, yes. Partly because Ice is so weak.
Rhyperior, maybe. Ground is also weak, until Groudon gets Precipice Blades. So Rhyperior could compete with Groudon, but neither is as relevant in the meta as Machamp, Blissey, or Tyranitar. On the flip side, a stronger Ground move wouldn't break the meta. Giving Mewtwo Futuresight or a good Psyblast would, giving Blissey a fairy typing probably would, or giving Machamp better Base Values (the things IVs are added to) would.