Ah - with Hebrideans, the grading and judging are completely separate, in fact the judge doesn't see how any animal has been graded.
I too have major concerns about showing certain sheep breeds, especially Primitives because of the, maybe unintentional, effect that the 'biggest is best' mentality has on the breed overall. It also means in ALL breeds that genetic diversity is low, even in breeds with many thousands of animals - only those few animals which do well in the show ring will be used as sires and with AI meaning that thousands of offspring can be sired by a single animal, some breeds have major problems with vast numbers of animals being closely related. In theory if they are all destined for our plates then it shouldn't matter, but some nasty genetic problems can be multiplied that way, as happened in Suffolks.