Q: Like, is V7 dominant because V7 is dominant? Or is V7 dominant because 7, 2, and 4 are dominant-function-sounding notes in the scale and they make up the majority of the V7 chord?
A: to be honest i have no idea why the word dominant is used to describe that particular chord. if anything really describes it most, i'd call it 'twangy', and it particularly describes the relationship of (for example) b and f notes (in G7), and more specifically, if you put G bass under that, it's called G7. the b+f creates the twang (due to their harsh relationship), and the bass on G makes it sound like a G major chord. with the twang