I'd like to see Nico and Lewis switch cars and see if that makes any difference. Maybe Nico's preferred set-up is what's leaving the gap between the two.
My guess is they would both be slower as each car is setup specifically to what the driver wants and needs.
Well what if what Nico thinks is fast, isn't. That'd be a revelation to him.....
Thats where Lauda and Senna were great. They had the know how to dial in a car.
Most teams let the No. 1 driver dictate the R&D path which has a lot to do with set up and feel. I wouldn't be surprised if they are driving near identical cars.
The differences you are thinking about are probably extremely minor.
Also, to touch on Joe's point, you have to keep in mind this is not the 70's/80's where the drivers set up their own cars, everything is decided and set up based on telemetry. The computer tells the driver if his settings are right for him or not. Not to take anything away from the drivers, but a lot of racing today is math.