Ok, clear, thank you. But have you ever considered, for example, following solution to bring it to the game?
We have 3 players, A and B in one alliance and 1 enemy player called C. A is dealing 60 dmg with his jacket, B is dealing 40 damage with his jacket (because of damage modifiers). They are atacking enemy player C and C is in the overlapping area of A's and B's jackets. The player C receives average damage so 50 dmg. Player A and B is using lifesteal food so they will get healed however player A will be healed more because his jacket deals more damage. In this case:
Player C - damage received: (60 + 40) / 2 = 50
Player A - damage to calculate lifesteal: 0,6 * 50 = 30
Player B - damage to calculate lifesteal: 0,4 * 50 = 20
So player A will heal with food as if his jacket deals 30 damage, and player B - 20 damage respectively. This way we don't punish players that comes in with jackets as second, third and so on.
If they were to do this then they would also have to do it for other weapons that don't stack eg Blazing staff, which could add more calculations.