I think I’m onto it, bear with me, sorry for double post and spam.
So Combat Instance Parent holds most of the functions in that instance, making it easier to mirror variables of that instance into the routine functions of combat.
I’m looking at fun_roll_attack flow:
%q9 -> pulls skill name for defining %q7 -> number of dice to roll
Setting %q7 evaluates %q9 to determine the value utilizing a quick function:
So its taking %q9 to see if its a number, and if it is, it leaves the value there. If the combatant is an npc, it takes the # value set on them, or if its a character, it pulls the skill value and does the ability_level global function to get the value … if all else fails a 4 is dumped in there to keep combat running but I imagine that never happens unless staff has blotched something in data.
So basically, if the weapon attack skill did a quick math, it would still work. But as you noted quickly, its not balanced; and this is understood adding an instance that stacks two skills is unbalanced.
ETA: hit save/post when trying to scroll down, edited to finish this thought