I think that DOACS interpretation is consistent with the acts of the legislature. The prior requirement (under the old law) was that a proprietary security officer who was unarmed would have a "PD" registration and would not need to work under a Class "B" agency or otherwise be captured by the requirements of Chapter 493. Under the old law if a proprietary security officer however was going to be armed, he would obtain a Class "D" license solely to be able to obtain a Class "G" license, and then otherwise be exempt from the requirements of Chapter 493 (except for of course having to meet the requirements for licensure).
At some point the requirement for the PD registration went away, but the exemption for proprietary security remained. The statute still makes it clear that persons who have obtained a "D" solely to get a "G" do not need to work for a Class B agency.
I wouldn't read too much into the fact that there used to be a "PD" registration and now there isn't, and perhaps this D/G thing is an unintended vestige of that. The reason I say that is if you look at the
1990 laws at the link you referenced you will see that then, as now, the exact same thing existed for proprietary investigators (without using the word "proprietary"). Then as now if you are an
unarmed investigator that works solely for your employer in an employer-employee relationship (and a bunch of other situations) then the chapter is inapplicable. See 493.6102(3) in both the 1990 and current law.
But also, then, as now, 493.6201(4) reads:
Class “C” or Class “CC” licensees shall own or be an employee of a Class “A” agency, a Class “A” and Class “B” agency, or a branch office. This does not include those who are exempt under s. 493.6102, but who possess a Class “C” license solely for the purpose of holding a Class “G” license.
Note that this language is the same as the language for proprietary security getting a "D" solely to get a "G" - yet there has never been a "registration" for proprietary investigators. This should make it clear that the mirrored language for security is not an unintended vestige.
Armed proprietary security is not uncommon. As I understand it all of the armed security officers providing security for schools (which is becoming a bigger thing now that the law compels either armed security officers or police officers at every school) are proprietary security. They do not work for a Class "B" agency, they work for the school district directly. They hold a "D" and a "G" so they can work armed.
As I said, the legislature did a bad job of implementing this exception, but the concept of a proprietary security officer or investigator getting the underlying license solely to get the "G" license to be allowed to work armed, but while still not being required to work for a Class "B" agency (in the case of security) or a Class "A" agency (in the case of a detective/investigator), has been around since the 1980 version of the law self-repealed and was replaced in 1990.
DACS would have no need to ask the AG for an interpretation of the law. They are given rule making authority within 493 and they know what the law means because it has been practiced this way for 28 years. If you talk to any security agency manager that has been around awhile the concept and boundaries of proprietary security and investigation are well known.
Your note regarding checking your carry insurance (or legal services plan) is a good one because you are right - most plans exclude any sort of "on duty" shooting.
Self Defense Fund has a plan specifically for private security and private investigators that covers you on and off duty (and is the same price as their regular plan). I switched from CCW Safe to SDF specifically because of this.