Absolutely not! The wire ring bites into the std head gasket, which if done properly, will give a very good seal around the top of the bores, albeit better technology is now available in the form of the metallic WRC gaskets (which weren't around at the time wire ringing was first done). My old EsCos (many years ago)was wire rung, and I never suffered any HG issues. You are correct about the surfaces of the block and head, but that applies to any sealing solution.

Wire ringing is not the same as 'Coopers rings', just for info.