Armor is a interesting mechanic however I think it just needs some more depth to it for players to better work around it and use it to it's maximum potential in firefights, both as a shooter and a player being shot.
**[Visibility]**
Vests should have some form of visible damage similar to how someone's helmet can be shot off, whether that be bullet holes or the vest being visibly torn out with some bright metal and ripped cloth just to convey to shooters that the other player's armor is indeed broken.
Players should also have a UI element similar to how your health gets depleted that just tells you your armor is broken/breaking in some capacity. Should also tell you when your helmet get shot off aside from just an audio queue.
**[Replenishment?]**
As for replenishing armor on players, that's a different story. I'm torn between either having engineers repair tool being able to fix players armor, which adds another class you need to either be or find in order to fully get back into a fight.
Adding it into Support's supply kit (and subsequently ammo supply drops) which then makes it so support gets a way to replenish its own armor on the fly possibly causing issues.
Having multiple classes have access to plate kits, which would then remove a different valuable utility to someone in order to just resupply after a basic firefight.
I'm uncertain the correct way to handle it honestly, but I don't think leaving armor breakable yet unrepairable is good for players trying to sustain in a prolonged engagement or just multiple separate engagements. Similar to how you don't want to be at low HP in your next fight
At the very least I would think visibly being told your armor is broken/breaking and being able to see when other players armor is broken would definitely help in determining if you want to get into certain fights