For "normal" players, this would be fine, in theory. However, there ARE players that win 25 rounds in a row consistantly. And this system would be the equivalent of giving those players the old exponential XP bonus back. We'd once again see people at level 40 eventually.
Well, so basically your statement is: it is better for new players, but still can be equal to the current system in some cases.
This sounds like a superior alternative to me
If someone REALLY wins 25 rounds in a row he MUST have taken influence on it, so he deserved it. Basically my suggestion would change reitiring from "a help for grinding" to "increasing the chance of benefiting more of your skills". Which sounds fair to me. Reitred characters still can level faster, but they actually need to do something for it.
I think those cases where someone wins 25 rounds in a row only by luck can be ignored, as they occur that rarely that they can't influence the overall balance.