Definitely jumping down a rabbit hole of theoretics which I don't really like the ideas of, but for the sake of conversation...
5.56 greentips (the AP rounds) used in Mogadishu resulted in a lot of people not going down when they got hit. Regular 5.56 creates more frightening wounds than what an AK47 can cause - this statement is not always gospel but the medical accounts are very supportive of it.
- Regular 5.56 rounds killed in one hit to the head or vitals.
- Regular 5.56 rounds killed in one hit to the torso in general (lower torso/shoulders included.)
- Regular 5.56 rounds did only half damage when target was wearing body armour taking them to a 2-hit kill on armour unless they land around it.
- AP 5.56 rounds killed in one hit to the head or vitals.
- AP 5.56 rounds killed in two hits to lower torso/shoulders.
- AP 5.56 rounds ignore body armour.
- AP 5.56 rounds have slightly increased penetration.
- AP rounds cost one point and are an alternative to tracers.
I'd strongly argue it'd be a perfectly balanced system and wouldn't favour one over the other. I must stress this isn't the solution I personally want to see (that can be found on page 3), but it'd be an interesting improvement over the current system. Furthermore, it allows the implementation of body armour which counters regular ammo as AP hard counters the armour at the cost of being less effective overall. All this really is, is a hugely scaled up version of the HE round system as aiming for limbs was incredibly impractical.
If in PvP I'd switch between based on how much armour I glance a visual of. I'd also equip armour if most of my team didn't or unequip it if most of my team did. This would absolutely be enough for me to change my playstyle and decisions reactively to my interpretation of what is happening around me.