The 30th century back then was 1,000 years from the 70's so it was reflective of the styles back then. The funny thing was I read a Grell interview not so long ago where he said he hated the Tyroc character and intentionally gave him a stupid costume. One only has to look at the other redesigns he did for the Legion or even Warlord and see that he gave almost everyone skimpy costumes at the time. Now these days Tyroc is wearing some boring red thing and he's bald.
