Win percentage shifts towards parity as an owner's drafting/managing advantage over other owners becomes less enforcable. A large chunk of the game is learning how to score runs efficiently. As team OBP goes up, so does the reflection of your ability to use it efficiently. Theres always a lot of parity at low caps, because the average team OBP is about .320.
So, basically there should be less and less parity as cap size increases. When, you get to $180mil, parity starts to increase a little bit again though, because the database is limited and you see a lot of the same players on teams. Still, however, I usually win 60-70% of games at $255mil, just on the merits of scoring a bit more efficiently than other owners.