They are??
As someone who wallows in ASN.1, Kerberos, and PKI, I don't find JWS so "gnarly". Even if you're open-coding a JSON Web Signature it will be easier than to open-code S/MIME, CMS, Kerberos, etc. Can you explain what is so gnarly about JWS?
Mind you, there are problems with JWT. Mainly that HTTP user-agents don't know how to fetch the darned things because there is not standard for how to find out how to fetch the darned things, when you should honor a request for them, etc.