well, to answer the topics question: your question is invalid. sfml is not a game engine and therefore there is no answer to "is sfml good enough for starcraft". it's like asking "is opengl good enough for a game like starcraft?" or "is iron a good engine for a car?". iron won't help you in your car. you first need to make an engine out of that iron (or whatever car engines consist of).
in the same way you first need to built a game engine around sfml. sfml only provides you with rendering, input, audio, networking and the basic OS-stuff (creating a window for example). therefore, sfml is not an engine (and it's not supposed to be). the stuff sfml does maybe accounts for a half percent of what you need for a game.
your question should be something like: "is sfml good enough to built an engine around it which would be good enough to programm something like starcraft?". then your answer is definately yes.
