I don't get it either. If I use Spring WS to provide the endpoints, how does it make it a monolith? It's always using the right tool for the right job but if one set of libraries are the right tools, why not use it across everything where appropriate.
One of the benefits of microservices are your ability to choose the right tools for each of them instead of a common denominator. I don't know about Spring WS, but if it makes harder for ie a Go microservice (or whatever makes sense for your domain) to talk to your service then I would consider it a liability.
