None, in this instance. The point may be that these regular police officers had those weapons to use and did use them in a situation where more mundane weapons like pistols and shotguns would have been more than sufficient.
I am not the cop’s biggest fan. However, the only limitation I would impose on them is that they shouldn’t have access to anything I can’t buy without special licensing (i.e. since I would have to have a class 3 license for a SMG, they shouldn’t have SMGs...).
The result would have been exactly the same with those as it was in the given situation.