Yeah, the Diplo victory (called a Political Victory btw) is pretty lame. I think true Political Victories are naturally lower scoring. I mean because the onyl reason you should get a Political Victory is if you and maybe 1-2 other races are left and they are pretty big. If you controlled 30% of the galaxy and still manage a Political Victory, you will have a lower score than a Conquest Victory. Not that much lower, maybe like 10-20% lower score.
I think that Political Victory scores should be nerfed something fierce. If you have 10 planets left and the other race has everything else and you ally with them, how the heck is that a victory. I suggest that Political Victories get a % of the total score based on how much Influence they have or # of planets.
Imo Political Victories shouldn't even be allowed in the game and they actually make GC2 a much easier game than it would be without it. I would make a longer post about it, but man I'm so lazy.