Here's my suggestion
First, rename AC to Dodge
Dodge determines your ability to react quickly allowing you to prottect beeter against area damage. And also determines your ability to avoid melee attacks
In game bonus:
Reduce any AoE damage (so any burst attack or explosion regardless its damage type) by a percent determined by the AC (Yes, it sound like DR, but only applies to some weapons)
The reduction takes place before the current damage reduction formula. So if a burst attack normally deal a base damage of 100 and target AC its 20 it will be dealing 80 damage then the other factors are applied(DR,DT, critical, etc).
At melee combat it reduce the max chance to hit of your opponent, but your melee skill will reduce this penalty by 10% of your skill lvl.
So if you have 15 AC and the attacking player has 100 melee skill it will have a final chance to hit of 90.
Now melee chance to hit its always 95%. With this approach your skills will also impact on this chance, so if the enemy has 25 AC any char with 250 melee will still have 95 to hit
Base AC = 5+LK/2 + AG
Armors modifiers:
-Jacket = 0
-Leather = -5
-Metal= -10
-Combat = -15
Traits & Perks
dodger perk:+10 AC
kamikaze: -10 AC
max AC= Base 20, +10 (dodger) = 30
Against a target with max AC
-A char with 50 in melee weapons will have 70 (95 -30 +5) max chance to hit in melee
-A char with 250 in melee weapons will have 90 (95 -30 +25) max chance to hit in melee
30% damage reduction may seems a bit too much, but you need a char with 10 AG 10LK + dodger and wearing jacket armor. Other option can be to have the bonus halved when you are standing, and the full bonus only while running.
Also this may probably require to buff AoE weapons damage by 10%-15%, which will be an intermediate value.