Are Ambulance Response Times to Slow?

Having worked in EMS, I know first hand that no matter how efficient an EMS system is, there are times when it will be pushed to the limit and people will have to wait for an ambulance to arrive. The question is: What is the standard? How often should an EMS system (or any public safety agency) be allowed to delay response times? Below is a video that discusses Philadelphia's EMS system and how it is regularly being pushed to the limit. Is this fair to the public for which we are there for?