Karl Malone is physical. He roughed guys up on offense and on defense. Oakley was physical. Rodman was a physical big.
Dwight doesn't do that. He swats shots from the weak side and dunks a lot, but he isn't a guy known for banging with his opposing assignment on defense and throwing them off. That is why Hibbert, Bynum, Kaman, Pau, and Duncan have gotten theirs against him and hindered him in the past by making him defend them in the post one on one and taking away his lobs since his post game has always been shaky. It is also why Sheed made him his bitch for years and shaq still can.
And I hope to god you don't think rebounding alone makes him physically imposing as Pau and LO pull them down with ease by simply knowing the angles, Love pulls down 15, and Bosh was pulling down double digits last year.