Cahin weapons and power weapons are still a bit too close in my opinion. So in an effort to give power weapons something to set them apart, what if they caused an armor debuff for a short period, preventing the target from refilling to maximum armor for a duration of 10 seconds after the last successful hit. Maybe a 10-15% penalty until the debuff wears off. Maybe chain weapons could do the same.
I like how Space Marine had weapons that were more effective vs armour than health, and vice versa. To that end, what if Chain weapons were less effective vs armour but better vs health? Power weapons could be better vs armour than health, or remain untouched. That way, Chain weapons could be the go-to for low armour/high health targets, while Power weapons would be better for more armour stacked targets.