It’s still a bit of a problem, even if it’s only providing that benchmark to quantify contribution.
For example, a Derek Lee home run does more for the Cubs than a Reggie Sanders home run does for the Royals, merely because the Royals’ pitching staff is more likely to give it back. To win on offense for the Royals, you’ll consistantly need six or seven runs, just to be safe. For the Cubs? Maybe only five or six to be safe. Also, Lee is in the NL, whereas Sanders is in DH-Land. Home runs are slightly more valuable when pitchers bat. It may be very marginal, but it’s a difference, and Sanders gets the same Win Prob. credit that Lee does for differently valued acts.
I think it all gets hung up in “contribution to the win or loss”—if it was just contribution in general, it might be okay to maintain the same benchmark from team to team, league to league. But if we’re measuring contribution to how the team did, the team needs to be somehow accounted for. If Derrek Lee were on the NL All Stars team, he’s almost as useless to them as a replacement player 1B, but if he’s on the AAA Iowa Cubs, he IS the show. He’s Babe Ruth in little league.
Is my thinking flawed here? This isn’t rhetorical. I have this sudden feeling that everything I know about Win Probability is wrong. :)