God yes! I would too. I've not watched a lot of Sullinger, but the times I've seen him, I wasn't blown away by his production. As a matter of fact, Robinson "ate his lunch" when they went head to head. I admit that I have some questions as to how his game will translate into the pros. He may do very well. I just don't want him with the Spurs.
The final point I'll make here is that at 36 years old, Duncan should not be forced to continue being the best shotblocker, rebounder and post defender on the Spurs. It's too much of a load for him. He needs serious help in those areas and there really isn't no one on the roster capable of helping him with the heavy lifting. Thus the need for more of an athletic, defensive-minded PF/C type, in the mode of a Bernard James, Robert Sacre, Henry Sims or Kyle O'Quinn.
The Spurs don't necessarily need more post offense. They will be much improved in that area with the likely addition of Lorbek. Instead, they are more desparate for help in the aforementioned areas where Duncan is declining. As such, the Spurs MUST get away from the undersized and underskilled bigs.