Tobirama is misunderstood to say the least, but to say he is a villain is a little too much. He cares about the new village they just built, the alliances, all of that. Granted, he still does have a deep hatred for the Uchiha but that's because he completely understands their nature and sees the threat there. He analytically and politically dominated them because, to him, it was still just Senju vs. Uchiha to the end.
So, Villain, no.
Antagonist, maybe.
Winner, yes.