I have a philosophy that chords aren't inherently functional; only notes are functional. Like, G7 isn't dominant in C because it's V7, it's dominant because B, D, and F are dominant-sounding notes in C.
sure. i don't really know what they mean by 'dominant' (that seems like a deceptive word to me) but yes i agree, chords are just made up of notes and bits of harmony. using letters to symbolize chords can be an extremely handy shortcut if both the writer and reader are thinking of it the same way, but it is still only an approximation of what the actual notes are