I don’t think that one can claim this is true, I once saw a friend who had a basic system installed at future shop, the installer ran the power wire and the signal wires on the same side of the car, and he ran 4awg wire thought the car but ran short on the end so he added a bit of 6awg wire onto the end with some electrical tape… yeah it sure worked…
I also saw an installer at an independent shop who screwed an amp into the side of a car with self tapping metal screws, these went straight through to the fender… it eventually rusted…