actually your putting the chicken before the egg.
You cant accurately figure out ac calcs unless you have reasonably close base dmg calcs. Your right that the formula doesnt work 100 percent of time, but id say its inn 90-95 percent of cases, the exception being low levels off the top of my head.
You dont have to add any more DB fields that im aware of because all you need to plug in are min/max dmg, which are already in DB.
The hard part is figuring and applying the ac/atk comparison to the base damage AFTER that

Because well never know the ac/atk of mobs well always have t olive with an approximation of it, but im fairly sure even there we can get far closer that where we are at now. Too bad i cant code at more than a beginner level :0
If there are any good coders out there that would like to work with me on it, id be interested.