How do you know that he hasn't spoken up about that?
How do you know that the Spurs haven't tried to get him more help?
Just saying that he wants help doesn't mean the Spurs can go out and acquire players who will accomplish that goal. And, it's probably relevant that with their limited assets available last summer, the Spurs went out and acquired at least 3 guys who they thought would be able to provide that help in the paint -- Blair, McDyess, and Ratliff. Saying that those have proven to be less-than-great decisions (other than Blair) is very different than saying that Duncan hasn't asked for help or that the Spurs haven't listened to that request.
In calling the man soft, in whatever context you claim to apply it, you sure do rely on a whole lot of assumptions and not very much evidence.