The big Lakewood WA police shooting where 4 police officers were murdered, the Oakland CA event where a few LEOs got shot and the big Pittsburgh PA shooting where a group of 3 LE officers were killed by a nutcase with a AK.
To me it's a smart move to carry at least 1 full mag with any type pistol. 17/19 rounds may be more than needed but you could also have a jam, problem or issue with the pistol magazine. When most weapons/tactics trainers check pistols 90-95% of the problems are mag-related.
As for the "panic" issue, I can agree with part of it. In the early 1990s I was through a training class with a early version of the FATS(a big video/CGI type use of force system). I was in a traffic stop with a beat up old sedan. The trunk started to shake and I raised my M9/92F type weapon. In a flash, a big fat guy holding a sawed off shotgun jumped out of the trunk. I fired off about 9 shots at the subject. In the review, 8 of the 9 pistol rounds hit the subject.
My MP squad leader got mad and started to chew me out for the response but I honestly did not feel my shots would be that big of an issue in a real after action review/investigation. The criminal had an illegal 12ga pointed at me and was at CQB/point blank range. It was valid to question the methods(9rds) but that is more of a tactical rather than legal issue.
In 2008, my armed security class instructor(a combat veteran and member of the state's security regulations-training panel) told us we should fire our pistols or revolvers with many rounds to create a "shotgun like pattern". This plan or tactic may have some merit but in a remote or rural area or job site an armed guard or PI may need to make every single round count. Even a 18 or 20 round 9mm/.45acp/.40 duty pistol could be used in a critical incident.
ps: If any TFL members think that some PIs/armed security officers should work in groups or pairs I say; not bloody likely.
Most security clients and contracts would give you a kidney or a lung before paying for 2 or more armed officers.