For the most part. I too spent my college years mostly in the electrical and industrial maintenance fields. Generally speaking, wire size determines ampacity and insulation material and size determine voltage rating. There are of course exceptions and derating factors for both. But most of them are far beyond the scope of anything members here will be doing.
If you have a piece of 18 awg stranded copper rated at 300 volts and 14 amps, going to 14 awg or even to something like 1/0 with the same insulation type will not increase the voltage rating any. It will just increase the current rating. Likewise going to a 600v rating in the same conductor would just be a change in the insulation. The size and type of the conductor wouldn’t change any, and it would still be rated for the same 14 amps.
Like you said if you go from copper, to aluminum clad copper, to straight up aluminum conductor you will see some differences in current rating. But that has to due with the conductor material itself. You would need a change in thickness or material of insulation to change the voltage rating.