well to get detailed this fancy tin coating is about 10x and steel is about 13-16x that of pure copper so ignore any skin effect and solder resistance. but that is getting into weeds.
sure not debating the point you raised from science ... but the statement that "it matters" in voltage drop in application here..
to be clear..yes to state a clear fact you are correct mathematically and in terms of physics..
AND to further just show that I am not insane.. with my home 'spectroscope' testing OEM wire shows copper in the wire where this "cheap" stuff is well just iron looking core.
but to suggest that it gives one hoot of a difference in practical application we speak of here ..is a waste of cash. (and laughable IMO)
the standard pinball Gi track is no longer then 4ft. there happens to be (with my test gear) .7ohm resistance on 4ft of "fancy" vs "cheap" so we are at a wash there.. (I had a win to the new wire at .5ohm likely because its not oxidized and this was far from an official test - just holding a probe tip ..mind you this isnt copper core probe tip either .. I didnt upgrade to 'monster' silver plated probe tips yet)
now that GI AC 6v and with mathematical voltage drop of less then 3%.. even if that mattered for most pinball GI that is typically incandescent which wouldn't matter on voltage in the first place! (for the roughly .2v loss) as the lamp will light with proper amperage under most any case (lets say 1v, but delivering 6A at 1volt is problematic for other reasons) lets pretend its LED's (where voltage is more important) then we have less amps and the voltage suffers less so again.. waste of cash. (IMO)
not even delving into the topic that the connection from the lamp base to the lamp, and the lamp in the base is just friction contact! (except for 555 which only has one friction contact)
that is why I wondered if your joking.. sure for a college classroom your correct but practical application is insanity. (IMO)
So .75c a foot or .005c a foot, your money your game your choice. the orginal post here was looking for budget GI wire.. people who choose to pay high prices for wire.. why look here? just pay your price and look down on us who did it cheaper.
AND as mentioned going to a lamp store will find you "lamp grounding wire" they have spools of it.. however it wasn't the same size (and its not tinned) and cost a little more.. so you can have pure copper gold under your playfield. hell get a solder bath and tin it yourself!