I'd actually say that Speedfreak was the most dangerous, as he absolutely mauled the Hulk a few times.
And Namorita was by no means overkill for Nitro. Even before he got amped up, he threw down with Captain Marvel and held his own against an early Genis and did some damage to Iron Man.
The problem with comparing it to law enforcement, is that the Warriors *weren't* law enforcement. They were a reality TV show, looking for ratings and allowed themselves to be compromised before they had a set plan.
Police, in a situation like this would get more leeway, because it would be understood that while they are trained and professional (ideally), shit happens. A private citizen screws a situation like this up, everyone would ask why they were in the situation in the first place.
Though, freakin' hell, the Warriors should have been shown as professionals and not glory hogs. Millar, as ever, went with the easy route.