a helicopter is no use if they don't have something actually on the ground that can quickly get to the criminals and arrest them. They use helicopters to direct the police cars on the ground so they don't lose the criminal. A helicopter on it's own wouldn't be able to do anything other than watch the criminals as they get away.
I think it's only right that the police have fast cars. If they have slow cars then it just means that chases will last longer and in more cases, people would get away. I reckon it'd also increase crime since people would know the police only have slow cars and they think they have a better chance of getting away with it.
