I’ve tested it with an idol that increases % physical, a helmet, and a weapon. All of them are increasing my warpath’s damage even though I have Apocalypse whirl. I’m not sure if it’s a tooltip bug or an actual damage increase bug though.
Edit: I’ve been able to test it on training dummies, it’s just a tooltip bug. It seems like the tooltip is scaling with % physical still and not % void damage, but in reality the % void damage scales the damage but % physical doesn’t. Makes telling what’s an upgrade difficult though.