correct, electricity has whats called a skin effect where it flows over the skin of the conductor, but with the high strand count wires I were using with 3-4k strands has too much resistance like you said and instead of them flowing more they just turn into giant heater coils and eventually the wire suffers enough damage until its nothing but a resistor and you get a severe lack of current flow.
My connectors and fuse boxes kept melting and I could not figure out why until I went with the 4/00 300 strand wire that I could barely bend. I could run and start 2 cars off of the wiring I installed.
im also using some 2/00 aluminum wire that is like 6 strands and that shit might as well be solid because I cant bend it, but I dont have to worry about melting it...
TLDR:
Best Conductors in order:
Silver (tarnishes/cost prohibitive)
Copper (tarnishes)
Gold (does not tarnish/cost prohibitive)
Aluminum (tarnishes/harder to work with/cheap)
According to the National Electrical Code tables, stranded always has more Ohms (resistance) compared to the solid alternatives. It's not much, but it's there. For example for 14AWG wire, solid wire is 3.07 Ohms per 1000' versus 3.14 Ohms per 1000'.
And as far as aluminum wire why would you use that for anything besides cost?
#14 solid aluminum is rated at 5.06 Ohms per 1000' and stranded 5.17 Ohms per 1000'. So for the same amperage you need a larger gauge Aluminum wire to match that of Copper wire.
Just for an example, (excluding all other factors like temperature, conduit fill, etc), to feed a 200 Amp panel with a copper conductor I could use a 1 AWG wire (rated up to 220 Amps), but if I were to use an aluminum wire I would need to upsize to at least a 1/0 (rated up to 205 Amps). This disparity gets worse the higher the amperage, you have to upsize more and more just to match the rated amperage of copper.
As far as why audio wire often uses fine stranded conductors, I'm not EE, but I can only speculate it has more to do with flexibility than conductivity.
Copper as far as I know is only bested in conductivity by silver, and by so little that that cost/benefit makes copper superior hands down. Aluminum probably the 4th best metal for conductivity, but it CAN make up for it in cost, though you may lose some of those savings due to the need for larger conductors, and additional labor to install it (it's much harder to work with).
Gold is worse in conductivity than copper, but better than aluminum. Obviously cost is a factor with gold, but (pure) gold unlike copper, aluminum, and silver, does not tarnish or rust.
