You should probably just consider the Yashica lenses on their own merits, rather than any supposed resemblance to Zeiss. Apparently there was a separate production line set aside for the Zeiss stuff in the Yashica factory, and only the Zeiss-branded lenses benefited from Zeiss's glass design, coating and QC. I have heard that Yashica designed (e.g.) barrels and electronics for some of the later Contax lenses, however. There were certainly some very nice lenses in the Yashica lineup - the ML wideangles had a good reputation, especially the 21, and I always had excellent results with the 50/2. This guy seems to like it too: