I often go with Statecraft, and gun for Industrialization as often as something else. Why? Ironclads. If the naval component is important to you, they are big. Also, it takes me a while to have enough paper to spit out diplomats. By then, I have enough factories/seaports to make the efficiency difference seem secondary. Note that I am comparing apples to oranges, because that's what the tech forces you to do. I don't think you should decontextualize it to a strict envoy vs diplomat comparison at that stage in the game.