The suggestion:
Any Damage Bonus UV negates Enemy Resistance to that damage, making it in effect Neutral damage (+ whatever the bonus is)
I am NOT suggesting a UV create Neutral to Weak resistance.
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This would bring new value to previously 'junk' UV's, in a game where Attack Speed and Charge time Reduce are almost universally better than Damage Bonuses.
It would also completely overpower those UVs, because you're forgetting about gear that gives similar UVs. Someone can deck themselves out in one piece of Deadshot and one piece of Valk gear and now their shadow weapons have no weaknesses.
The point of a UV is to give a minor bonus. Having a Construct UV on a Piercing weapon isn't optimal, of course, but that's part of the luck of the draw. Some people like having a UV to help balance out a weakness a weapon has.