90% is actually a really good estimate, I think. Before championship mode came out, I'd won around 63% of my matches, and after climbing to G1 I'm up to 70% wins. My old longest winning streak was 21 wins, a week or two ago I saw it had increased to 34, and now I'm in a 41 game win streak that's still going. The problem is that when I fight someone good, win or lose, I'm forced to move on and it's unlikely I'll see them again. I used to like playing good people in ranked battles over and over.
My stats for championship mode so far:
G3 - 26 wins, 10 times runner up, 4884 max CP
G2 - 107 wins, 23 times runner up, 63571 max CP
My record over the past 30 tournaments is (seriously, you might not want to look)
:lol
G2 just became steadily worse. No surprise my record is actually better than it was in G3, which was loaded with good players for the first weekend. Most of my losses over the past month have been in player matches, and I don't play those nearly as often.