> that SOAP pain
The pain you're referring to is relative to the language you used and when you touched it. SOAP is a comprehensive and we'll defined specification and when implemented properly you forget it's there because it just works.
After about 2003 major vendors had their implementations locked down pretty well. In Visual Studio you just implement a basic controller and the remainder is configuration. If you wanted to consume something from Biztalk, PeopleSoft, any Oracle Product, or any other Enterprise product you could just add a service reference to a WSDL URI and a tool would generate your interface classes and DTO classes for you in your language of choice.
In the Open Source world things were very different. Whenever I would provide a service to be consumed by a vendor, I would provide reference implementations in C#, JAVA, Python, and PHP. I would spend about 15mins on C# and JAVA, then the rest of the day fiddling with Python and to a lesser extent PHP.
PHP and Python have had SOAP libraries for a decade but they require considerably more effort to even consume SOAP. I have never tried to stand up a SOAP Service with them but I can't imagine it's any good.
Around 2012 I remember working with a partner company that was using RAILS for their platform. It was an absolute nightmare for them to integrate with our existing SOAP service layer. SOAP protocol libraries were the least of their issues. No client certificate authentication in their HTTP libraries. No serious XML support. They wrote their own implementation from scratch.