Tamba Hali's rush-defense has been mediocre/average with a spike in improvement last season -- don't say he is "just as good of a run-stopper" because he flat out is not. Hali is another hybrid player and a guy who depends on burst as he is a slow player if asked to race (4.9/40); he is not going to be as good roaming against the run as a guy who flies about the field with the speed of a cornerback.
Von Miller did not miss a single tackle last year. Per PFF, whose calculation you can take or leave, he was the highest rated defensive player in the league. Why? Because he can make tackles look like tools, stuff running lanes, and roam to track down the ball with ease. His ability to both pass rush and stop the run is what puts him up for debate as the best. Ware, Allen, et al, are not exactly the best of comparisons, at least with not first taking into consideration these guys often play at the line in the DE position. Miller's competition comes from Suggs, Matthews, etc. I think he blows the one-dimensional Matthews out of the water; with Suggs there is debate. With Hali... Hali is a great player, but Miller's impeccable run defense and range on the field clearly makes him a better linebacker in my opinion.