choose the AI -> Y menu -> Find the botton that said something like AI control.
Now you are controlling the AI. Just go to the arsenal and pick whatever you want.

I am well aware of being able to forcibly equip my own AI squad members, but the issue rises from non-squad AI such as garrisoned units spawning with sub-par gear when superior equipment is readily available.

train them / select more appropiate classnames

Well, they're now level 10, with several versions of the USAF level IV vests unlocked, and they still absolutely refuse to spawn with them. At most, they'll spawn with some AFRF level IV vests that I haven't even collected a single copy of yet.

I'm not sure how selecting different classnames will work when I garrison an area with a healthy mix of each class to no avail.

vest inclusion is on roadmap, only weapons and other stuff

Hey B, other problem I have with this is that the AI aren't using any actually decent AA weapons. I got unlimited launchers of a few types, but still struggling to do so with Stingers and Javelins. Using RHS, obviously.

I was wondering what the default # of stingers and javelins was to make them unlimited... and will AI ever spawn with them?

I have AI training at level 20, and every single invasion we get to is a nightmare because the enemy helicopters simply can't be shot down, even with a few static AA emplacements if they send any attack helicopters.

Try buying AA vehicles ( if using RHS, its a Zu-23 ) and putting them around the outposts and factories.