Jirass was made in the sixties using the then Godzilla suit at the time (Tsuburaya was the Head of Special Effects for Toho, so he allowed it) and modified to be a different monster. Zedus came out in 2000 and something. Calling him a Godzilla/Zedus hybrid, is a terrible comparison.
Jirass is supposed to be a reference to the Godzilla series as shown by the ripping off of his frill and the respect Ultraman showed him after his death. Tsuburaya had used and modified Godzilla Kaiju suits before and most would hardly be recognized from where they came from. So his resemblance was intentional to serve as a homage. Calling him a 'Faker' undermines the point that he was clearly serving as a homage to the Godzilla Franchise