10awg vs 12awg... the effective quality of the wire has to do with the overall surface area of the strands it has in it. The current does not flow in the strands of wire in it but along all the edges of each strand of wire it has available.

So a 12awg with hair thin strands in it will be better than a 10awg wire with thicker strands in it due to the effective surface area. This is why nobody buys their wire at Home Depot.

You can think of it like the difference between trying to burn a bail of hay or a block of wood the same size. The hay has more surface area to ignite and will burn much faster and easier.