This is not Shaq's fault at all. The Suns were not going to be able to beat the Spurs before they traded for O'Neal, and not with him now.
The Suns' problem is an inability to guard both Parker and Ginobili. Exploiting Shaq's lack of movement is going to happen with Duncan, just as it would against just about any team the Spurs play, not because they are playing the Suns. Duncan, mainly, and Parker can pretty much do that against any opponent. What the Suns are unable to contain is Parker. When Shaq ends up being the final answer between Parker and the basket, somebody on the Suns is failing his job, and it is not Shaq.
But if that were the only problem the Suns had defensively, it might be overcome. With the added problem of Ginobili, they have no answer at all. Somebody has to slow down Manu and that has not been happening. As long as both Parker and Ginobili are practically unguarded, or unguardable, what Shaq can and cannot do is hardly important. HE is not supposed to do that kind of contain work on guards.