hard to know if a purple and a red are worth a blue and a silver if the elo is evenly balanced

There are probably multiple problems with the balancing algorithm, for example http://zero-k.info/Forum/Thread/36555 , to quote "The results indicate that the larger team does have a moderate advantage depending on team sizes and the exact model"

That's on top of any potential issue of rank distribution, because I think in this case the problem was that the distribution of the two teams was so "different" (basically "best ranked + lowest ranked" versus "middle ranked")

Now, I don't think that changing it without a through analysis is smart either. I have seen games that I thought they were worse balanced than this one and the result was opposite than what I thought initially...