We have too much alloy in the wrong places. Wheel rims need to be light but hubs could be steel or a less easily corroded alloy. Brakes are alloy but stainless sleeves in the bores would solve need to change seals every few years.
Brakes could also be (a lot) smaller if they used powered hydraulics then the excess weight of steel or iron calipers would not matter. The weight of a small hydraulic pump is minimal and could be driven off the alternator belt. It could be used to drive other stuff like on the fly ride height. Hmm sounds like another French car.
Engine parts are an issue. Car engines dont need to be especially light and dont spoil the car if they get rusty marks on the block. Ditto the back axle.