Alright.
I still think it is (clearly) a nerf to Dual Wielder that you can't wield two non-Light weapons. I get that Nick requires the Light property, so for optimization purposes you would always want to have a light weapon in at least one hand. Personally, I think Nick should not be tied to the Light property, but that's another separate gripe.
Edit:
Here's how I would have written a 5.5e Dual Wielder feat.
Dual Wielder
Prerequisite: Must be proficient with at least one martial finesse weapon, and 4th level or possess the Weapon Mastery feature.
You may use the rules for dual wielding so long as both weapons have either the light or finesse property, and you can make the associated additional attack as part of the Attack action, rather than as a Bonus action. This allows you to use your Bonus action for something else, if you desire. Further, any finesse weapon you wield may use its normal mastery property, or Nick, but you can only make use of one mastery property each round, chosen when you attack with that weapon.
You also gain a +1 bonus to AC while wielding two one-handed weapons with either the light or finesse property, and any time you would be able to draw a weapon, you may draw two one-handed weapons, so long as each weapon has either the light or finesse property.