For many years, I have known integration via WSDL, only to see the REST/JSON trend appear with false good reasons and real unknown reasons.
Why so Much Hate on WSDL?
WSDL offers a very strict interface contract, where any failure to comply with this contract generates errors. This means that when you want to add a field, if one of the two integration stakeholders has integrated the new field "too early," nothing works anymore. Of course, that's when your WSDL library is the same on both sides because how many times could we not integrate anything because we had two different engines on both sides? I'll let you imagine the meetings when we had to find a solution...