Cap'n'proto and ASN.1 require a schema. Gzip compression means the content has to be decrypted into json and then parsed into a native representation, which probably requires more memory and cpu than cbor deserialization.
That’s right. In addition: CBOR can’t automatically compress field names, since those are strings which need to get fully serialized. gzip can compress them too, so it has a chance to trim the size of data further down in exchange for the additional cost of a 2nd encoding.
Cap‘N‘Proto, protobuf and co can replace field names by IDs as indicated through Schemas and will thereby most space efficient in general.
