It doesn't matter if it's a lower standard.
It does matter if it is a lower standard. A DD214 is your discharge and proof of service. Just because you do not have submit it and can simply check a box that you served does not change the fact the state is crediting your service towards firearm competency.
And I think you wrote that the current DD-214s don't show any weapons qualification, so states that specifically require proof of handgun safety training won't accept a DD-214.
I actually find it amusing that you only have to sign an affidavit. It is very clear that many states have no idea what the Military is about.
I found it hilarious and a nice illustration of the ignorance when I asked about SFARTEC.