“LE says the security guard reported what happened on his radio. So LE knew where the shooter was when he started shooting, yet they did not in any way engage him?”
You skipped a step. If the security guard used his radio to report what happened, then he reported it to others at MGM. He would not have radio communication directly with police (I doubt that anyway). The question is, when did MGM report the location of the shooter to the police?
“They are telling us LE got there shortly after shooter started firing into crowd...they waited until he quit shooting and then waited for around an hour after he quit shooting before breaching the door and entering the room.”
I have not seen this. The reports I have read stated that LE arrived on the 32nd floor shortly after the shooter had already stopped shooting.
You are right, the MGM may not have notified LE right away, though for an active shooter you would expect them to.
So if they didn’t notify LE right away, why wouldn’t they? What reason could they have?