I took a fast look at the Yankee stats with and without Matsui, with and without Sheffield, and with and without both.

I think that this will illustrate my point:

Code:
      
      Matsui                  Sheffield                  Both
   With      Without        With     Without        With      Without
 W-L   RPG   W-L   RPG   W-L   RPG   W-L   RPG    W-L   RPG   W-L   RPG
-
19-12  6.3  16-14  5.5  19-11  6.8  16-15  5.0   24-13  6.5  11-13  5.0

"Difficult....not impossible"