I think that a point about leadership is somewhat injured by bringing install base numbers in as the judge of winning. In partcular, it undermines the degree of leadership Nintendo had during the N64 and Gamecube eras, where it made several influential innovations in both hardware and software. I certainly agree that a healthy Nintendo is important to maintaining that, since the response to an unhealthy Nintendo has been calls for them to stop innovating and simply follow whatever happens to be drawing the most growth at this moment.
I do think that the relative parity of the last generation is an interesting phenomenon, and I think it speaks far more loudly to the co-leadership of all the companies involved. Each took bold steps in various new directions in such a way that many core gamers wanted something from all three. This is why, in many ways, Xbox One's steps down to match Sony don't bode well for it, since it is transforming from a position of leadership to an also-ran, whose selling points are "we do that, too".
I think it is far too early to make any calls as to the outcome of the current generation, as it is still really trying to establish itself. It's possible that we could have another three-way tie (although I'm a bit doubtful about Xbox because of their messaging (current, not the previous controversy). And so long as development for Wii U manages to expand and maintain a profit so that their attitude toward leadership is not compromised, Nintendo will exhibit leadership, regardless of it's numbers.
