Your original point was that a major actor will not play Bullock.
Now, you are saying Fox was not a major character in the books.
But, my original point was that Fox was played by a major actor, so Bullock could be too.
There is a different size in role and importance with folk like Alfred and Fox, to Wuertz and Ramierez, like you were automatically comparing Bullock to.
So, let's get the rankings right, there are 3 we are dealing with, not two.
Major roles - eg Batman, the Joker, Dent etc
Major supporting roles - eg Fox, Alfred, Gordon etc
Minor supporting roles - eg Wuertz, Ramirez, Flass, etc
If you are saying that Bullock would automatically be included in the minor roles, I would think again, Especially when we will have a 3rd movie concerned with cops being after Batman. Gordon being the only cop who will not be into the task, and Wuertz and Ramirez being dead and out of action.
bottom line, if Bullock was a major supporting act, it would not be strange to think Rourke could play him.