His mistake, and same for any cop anytime, is that he still retained command of the incident while he was hands-on. At that moment the role of incident commander should be automatically passed on to someone else. If all 4 cops are hands-on the scream some code for that to your dispatch line & they must follow up with reinforcements.
If there had been 12 cops there then no cops would have gone to prison. There was only 4 there. They were short staffed. And none of their chain of command has been held accountable for that mistake.
Yeah, it would have helped if Chauvin called for backup.