I would be very interested in pokemon win statistics as well. The fact that the ladder pairs even-skilled players makes the statistic more pertinant, if anything. With player skill somewhat controlled for, you can get a glimpse at a pokemon's true utility.
Even so, the information would still be useless. You won't know if it was really
that Pokemon that was carrying the win, or if one or more of its teammates did most of the work there, or if it was mostly even (and going further, you don't know
why the Pokemon that did most of the work did so; was it mostly because of good prediction, which frequently led to certain Pokemon coming in, and others not needing to, or perhaps the inverse, and some misprediction went down in those matches, causing certain other Pokemon to need to come out. This sort of stuff the statistics would have no way of telling you, making it's usefulness quite questionable). You also won't know how many of the matches were won simply due to stuff like bad team matchups, and so forth.
The key point though is that you don't know why those Pokemon won those matches, and how much of the win in those matches was even due to them, and not their temmates (their's no way of knowing how much of a role they all shared in the wins, meaning the true role any Pokemon played in achieving that numbers of wins is completely unknowable, in effect meaning the percentage really wouldn't have much actual meat behind it).
Putting all this together, the information wouldn't be telling you anything of use due to the inability to factor these things out, so I don't see the point in it being compiled.