Seriously, I just don't understand how can you described the benefits of CBOR and claim that they are its drawbacks.
Yes, you have to read the documentation of your encoder/decoder to understand what tag values it maps to your programming language's objects, but if you need to encode or decode those same values with MessagePack you'll have to define your own format for them and document it. You just moved this problem up the stack, but with an ad-hoc format.
Separation of "null" and "undefined" is for full JavaScript support. Before C99, C didn't have boolean type, but you wouldn't complain if serialization formats had them, would you? Same thing "undefined": while it's useless in most other languages, it's useful to have it for JavaScript.
I don't like float16 too - they took 19 lines of decoder code to support (no need to support it in encoder) — but it's the same situation as with "undefined" — some people need it.
Yes, you have to read the documentation of your encoder/decoder to understand what tag values it maps to your programming language's objects, but if you need to encode or decode those same values with MessagePack you'll have to define your own format for them and document it. You just moved this problem up the stack, but with an ad-hoc format.
Separation of "null" and "undefined" is for full JavaScript support. Before C99, C didn't have boolean type, but you wouldn't complain if serialization formats had them, would you? Same thing "undefined": while it's useless in most other languages, it's useful to have it for JavaScript.
I don't like float16 too - they took 19 lines of decoder code to support (no need to support it in encoder) — but it's the same situation as with "undefined" — some people need it.