The Shaq comparisons are completely inapropriate. Diesel is 4 inches taller and 100 pounds heavier than Howard, and at one time moved just as well. He was a dominant post scorer with a go to move (the drop step), as well as a very reliable jump hook.
He may not have blocked as many shots, but remember, during his peak there was no such thing as defensive three seconds. He could camp out in the paint, and people would not dare enter.
Finally, he was playing against some all-time greats and some all-time goodds in the paint - Duncan, Hakeem, Ewing, Motumbo, Smitts, Mourning.
Comparing Howard to Shaq is like comparing Mullins to Bird. All-star versus all-time.