More aero, less weight with DIY carbon fiber

[Logic]

Better aero is nice, but for Urban driving; less weight is king.
How about both DIY!

How to: Carbon flat floor: half the weight of Aluminum.

https://www.youtube.com/watch?v=qrSBnksPOdY

DIY Carbon roof: 12 to 3 Kg:

https://www.youtube.com/watch?v=Nq6B7wvki8Q

DIY fenders, bonnet, splitter, etc-etc:
https://www.youtube.com/@RuskiWeldFa...carbon%20fiber

A thought:
What happens, economy wise, when you take one of these lightened, aero modded cars and drive it slowly/economically..?
I have a feeling that, downforce excepted, all the weight vs aero testing etc is already done for us by this crowd and you end up with far greater Combined Cycle economy.