To early for a football game so here goes...
The current carrying capacity of a wire is not determined by the size of the copper or aluminum conductor. It's the insulation! Using building codes for example, code says for a 30 amp circuit use a #10 gauge wire with something like THHN insulation. What that means is at a 30 amp draw the insulation will not degrade, melt, etc. NOW, hang a bare #10 wire in free air between two post. Feed it current, lots of current. See how much current it takes to melt that #10 wire. I'd say you will be surprised.
Car manufactures do not use building codes for automotive wiring. The first time I really noticed this was when I was installation a Spal electric fan on my Hotrod. The instructions said it needed a little less than 20 amps. Sounds like #12 wire by building code standards right? The pigtails from the motor were #18 at best. What the hey, I said. I wish the rest of my car ran as good as that fan.
No doubt you need good wire with good insulation, clean connections, etc. But you will see what many would consider undersized wires all over your ride.
I run a #8 wire from my high output alternator with a fuse link. Some people hate fuse links but I still run one. As for insulation I only use GLX type which is cross-linked polyethylene.
I don't think I really answered your questions but maybe someone smarter than me will.
