You couldn’t be more incorrect. Nationwide, the first one or two cops are trained to immediately move towards the shooter and engage him to neutralize and/or fix him in place.
All the perimeters, swat, supervisors, etc you mentioned arrive and respond to where the FIRST cops are and bring a better follow on response. No department anywhere teaches what you said and you cannot back that up as a policy from any department. And yes, department SOPs are public and available nationwide.
A good friend of mine is a former SRO, retired a couple years ago. His training was go after the shooter above all else, run to the scene. They know any wasted time means more kids getting shot.
So were the cops in Broward ordered not to follow training or did they just sleep through it?