Someone once gave me the following advice:
1) Keep your armor ready to throw on by itself, without extra gear attached. 2) Have slings attached to your weapon-specific mag pouches (like bandoliers) to simply throw over your shoulder as you see fit in the moment.
If you only need a handgun in the moment, you won't have AR mags weighing you down. Only grab what you need.
Secure your mags pouches hanging downward (so you're pulling down on the strap around your neck).