[marcosdumay]

In practice, SOAP was the one that brought the best functionality.

What is telling because it's a badly defined beast that mostly doesn't work. But it did the type checking, automatic (client) endpoint creation, self-documentation, reflection-based (server) endpoints, support for lots and lots of languages (as long as you don't use something like an array)...

People keep promising new protocols that do one or two of those things on the modern world, but they always fail to deliver. AFAIK, the last promise was grpc, but doesn't even use a widely supported subset of HTTP so it has no chance of ever going anywhere.