WHY They Didnt go in all at once
maybe this can clarify it for some of you
1.duvall is trying to keep his men alive thats why hes doing it in the first place
2.roenick has positional and tactical advantage
3.the more of his men that are killed the harder it is to cover it up
4.he has no idea how many people are in the precinct
it could be 1 guy with a pistol or 20 with rocket launchers
and obviously he doesnt bring in the helicopter at the beginning because its not like he can just ask for it