This sounds like protobuf and gRPC. Is that a close analogy?
I hate that for years the concept of RPC was equated to XML which in turn equated to some implementation of the (XML based) tool and then a whole lot of distracting discourse around XML vs JSON, we kinda do still have that these days with yaml vs whatever.
The tooling around these paths is also lackluster by comparison if you're using something like Visual Studio.
I'd rather fight XML namespaces and HTTP/1.1 transports than sort through the wreckage of what "best practices" has recently brought to bear - especially in terms of unattended complexity in large, legacy enterprises. Explaining to a small bank in Ohio that they're going to need to adjust all of their firewalls to accommodate some new protocols is a total nonstarter in my business.
WSDLs and XSDs done right are a godsend for transmitting your API spec to someone. I use .NET and can call xsd.exe to generate classes from the files in a few seconds. It "just works" if both sides follow all of the rules.
The APIs I work with would be cartoonish if we didn't have these tools. We're talking 10 megabytes of generated sources. It is 100x faster to generate these types and then tunnel through their properties via intellisense than it is to read through any of these vendors' documentation.