I stand by my description of the correct way to wire a car.

Alt noise gets kept out of the car chassis circuit, by the alt current never being allowed to exist in that circuit. If it's not there, can't make noise. Just like the car in the lane next to you can't put alternator noise into your radio. (ignition noise, .... different matter altogether)

Yes it is entirely possible for the frame or unibody chassis to offer lower resistance than a piece of wire; almost obligatory in fact. However that leads to other problems. Notably, it increases the number of connections, and the ones that it adds, involve steel, which rusts. Therefore no matter how good you get it to be, it isn't likely to stay that way for long.

About 99% of all electrical system problems occur at the connections. (such as the above, a bad connection where the starter connects to the block, although I gotta admit, I DID NOT see that one coming) Making sure that there's as few of those as possible, and that they're in locations (electrically) that prevent them from interacting (alt noise being a good example), and that they're made in the most stable and reliable way possible, is usually the "best practice" for building ANY electrical system.