I/community needs a list of the items/abilities/spells that operate on weapon damage range (before the additive modifiers are added) ..
( with weapon min damage = weapon max damage - damage roll RNG is eliminated and we (community) can quickly reverse engineer damage formulas and where each and every item/talent/ability/spell effect factor in without having to keep begging busy DEVs to give crumbs . Armed with that knowledge community can then easily test all damage related factors and be able to provide meaningful bug reports .. You've got a big bunch of smart lab rats willing to help - use them !! It is going to happen sooner or later anyway .. )
Only one I'm aware off currently is Fighter ability "Confident Aim" – "the minimum damage for any melee weapon they use is increased by 20% of the range between minimum and maximum. Sadly that is not enough to "close the weapon range gap" for any of the basic weapons ... (gap bigger than 20%) .. Perhaps there are unique weapons in the game with damage range tighter than 20% ..
Alternatively (if no such item exists (both Diablo 2 & 3 had them ) ) a modder could alter "confident aim" to provide higher bonus (ex 100%) (still could only test fighter abilities) , a custom testing weapon with wmindamage = wmaxdamage or better yet a "testing ring" that adds certain amount to weapon min damage (or subtracts certain amount from weapon maximum damage ) ..
PoE community, how long will it take you ?
Will the devs cooperate ?