Using the Sling Post Servlet to create nodes when you are in a Process is to add overhead, not avoid it. The turnaround to create and send a HTTP Request to let the servlet take care of it is in my humble opinion to go over the river to get water. It is roughly the same amount of code to convert from JSON to http request than from JSON and directly to node. And you don't have to mess around with HTTP Requests.
And, the solution with HTTP Request is harder to test and maintain.
/Ove