But I've asked it now, so if It wasn't enough I would go with some other library.
I have a feeling you don't even know what you are asking for.
What is "enough" for you?
What would you need in a library to make it "enough for making MMO game"?
If you can answer this one question precisely, then we will be able to give you a simple yes/no answer. If you cannot answer this question precisely, then you yourself don't know what you consider to be "enough for making MMO game" and your question is unanswerable.
We won't tell you what you need for making an MMO game. You should know that yourself. We will simply tell you whether you will find what you need in SFML or not.
So maybe now you can finally ask a question that we can answer and be done with this discussion.