The problem with Soriano is that the Cubs' LF OBP is 24th. Most of the teams behind the Cubs in LF OBP (Dodgers, Angels, Twins, Mariners, Blue Jays) have had complete disasters in LF this year. Since OBP is the more important component of OPS, the fact that Soriano is so poor in that area (.296) outweighs his positive contributions on offense.
You evaluate his defense differently than I would...he looks every bit as bad as Adam Dunn to me. He's scared of the wall, looks tentative on everything, gives the other team extra bases much more often than an outfielder should, and doesn't have any kind of speed or range. He cannot handle playing in the field, and shouldn't be allowed out there after this season. Basically, he doesn't do anything well at all anymore except hit the ball out of the ballpark.