I don't see why you would call Chauvin a bad cop on the basis of what he did in this case. When a subject resists, all cops are trained that the first thing they have to do is regain control over the subject. Floyd was six foot seven and a bouncer in a nightclub. It took four cops to finally get control of him and wrestle him to the ground. Once he was down, the cops restrained his head and hips in ways calculated to do no serious damage. Nothing Chauvin or the other cops did to this point was wrong. The alternatives would have been to taser him or try to force him into the police car by brute force, both of which would have seemed more dangerous. When Floyd stopped struggling, the initial presumption was probably that he had surrendered and in the stress of the moment it took a minute for the cops to realize something was wrong. In fact, he had not merely lost consciousness but had suffered sudden cardiac arrest and was already dead.
As I said before, it is possible to make only a very weak argument for negligent homicide. If they have even a halfway decent lawyer, it is very unlikely that any of the cops will be convicted of any crime, and then there will be another round of protests and rioting, and the cops will have grounds for federal civil suits against the city and state for their outrageous behaviors.