I do, because the +10, 0, -10 bakes in the position they play. A LF whose ten runs worse than the average LF hurts you just as much as the SS who’s 10 runs worse than the average SS. Of course, a -10 LF has to be REALLY bad, since he gets fewer chances than a SS gets. But the impact is the same.
And obviously, in my hypothetical the offensive/defensive surplus/deficit zeroes out, but it doesn’t for most players.