Your analysis is correct. Thank God the shooter was not adept. I have been a shooter for over 50 years. I could have made that shot accurately with ease. In addition he selected the wrong weapon, again Thank God.
The real question is how he was allowed to get in a position to fire on President Trump. Their were no drones in the air that would have identified the shooter immediately. The secret service has drones and local law enforcement offered the use of their drones. There were no drones in the air. There is only two answers to this. 1. Incompetence beyond belief or 2. willful negligence.
I believe it was willful negligence designed to appear as Incompetence.
The lack of any Law Enforcement drone, be it Secret Service, Pennsylvania State Police or local City or County , is mind boggling . They can not be that inept, it was planned.
I have to wonder what, if any contingency plan the SS has to counter a First Person View aka Suicide Drone attack ? Zero ?
Actually I suspect a third answer (3. Complicit.)