a700, you are missing the point on the positional argument.
Suppose a player is going to hit .300/.370/.490, and he's going to do it every year. Your argument is that since he's the same every year, then he loses nothing in terms of offensive value. This is wrong. He loses nothing in terms of offensive "production", but "value" is another matter, one in which the position a player fields has relevance, because value is relative, so you have too compare to averages.
Now, suppose he's going to be playing CF for your team. With that offensive line, he's well above average for the position. Move him to 1B and he comes back to the pack. The team no longer gets above average production from a premier position and instead gets closer to average production from a position where it's easier to find a bat. This is the lost value.