Nothing in what you wrote, had she said it, would have made the police get there any sooner. Read what you wrote. You didn't mention a threat, you didn't mention danger to the children. You basically said that the father is being a disagreeable jerk, and is breaking the rules of child visitation.
The social worker can't tell the police that there is a threat if she wasn't aware of one. What you describe happens more than you'd probably ever want to know. People whose children are taken into care often antagonize the social workers who are in charge of that care. If this had stopped at the father opening the door and the kids being given back to the care of the social worker, it's doubtful the father would have even been arrested.
This man slaughtered those children, then blew up the house. The social worker didn't know it, though, until after the fact. She didn't have anything to say other than what she actually knew. She can't make stuff up and create a dangerous situation where one doesn't exist - if she did, would you want her to do it in the 99 other times this happened, but the kids come out 3 minutes later, unharmed?
I know a couple of social workers, and what they go through could make you cry.
Just for your information, I know fully aware of how the courts and children services operate. My own personal experience in gaining custody of my niece after the suspicious death of her mother taught me all I need to know. We went through six years of a nightmare with courts and inept social workers. They outright lied, forged documents, fell asleep in court, missed appointments, faked the credentials of the court ordered psychologist, one of them even slept with the biological father who happened to be a murdering psychopath. This woman on the Powell case had to ask the 911 operator what she should do. Then when she smelled gasoline, she was worried about moving her car. I read the 911 transcript, maybe you should too.