Jibaku
Who let marco in here????
It's not about "making Sucune an absolute zero blaster OHKO machine". It's about the Luxury that Sheer Cold provides in addition to its regular role. Suicune's most common role a a general physical wall does not appear to be compromised by this addition, and it often has 2 relatively free slots to throw in Sheer Cold (Scald/Ice Bear or Icy Wind/ and 2 of Rest/Sleep Talk/Reflect/Roar/Mirror Coat). Now it simply has an extra option, and a terrifying one at that.I don't really get why you'd use a Rocky Helmet with Sheer Cold, since the chip damage you accumulate with the helmet is wasted when you just OHKO stuff with SC.. I'd have thought a ChestoRest or RestTalk (with Leftovers) set would work better with Sheer Cold.
Of course you could make Suicune a dedicated OHKO machine, but that removes some of the reason why Suicune fits on virtually any team archetype.