Is a custom binary format that much more efficient than a gzipped human-readable format? If not, then it makes all sense to have a mostly universal decoder inst

Is a custom binary format that much more efficient than a gzipped human-readable format? If not, then it makes all sense to have a mostly universal decoder instead of a hundred different ones, especially since decoders of custom binary formats has traditionally been a major source of security vulnerabilities and other bugs even when those decoders have been written by skilled people and used in production for years.