Doubts about Roman Numeral Analysis and Music Theory

Having read the thread “Minor Keys, Roman numerals”, it questioned exactly something I was recently wondering and urging to ask. I’m not experienced in music theory, but, by logic, I can’t seem to help but find it all strange.

Why is the cadence Ab - Bb - C shown as bVI - bVII - I in the C Major scale, but VI - VII - I in C Minor? If the goal of this kind of analysis is to emphasize functional harmony, why do the functions change? It masks and makes a mess out of its principles, at least for me.

For example, I was taking a look at the Locrian scale. I know it does not have much practical use for cadences, but its “allegedly” V chord does not function as the basic V - I cadence (because it’s really a bV chord in its parallel major scale). As it is, this Roman Numeral Analysis scheme achieves nothing in trying to unify music theory, because I was under the impression that V chords may always cadence to the tonic chord, which is not the case with the Locrian V.

That other thread discussed that this is just a difference in notation. But with this in mind, I feel there’s another thing that bothers me. It seems as scales and modes are not really that useful. I mean, music can borrow from any mode at any time, and, sometimes, choosing a mode in which to analyze a music is troublesome. Perhaps it would be easier if “scales” and “modes” coalesced into just “tonic”; that is, you could categorize music just by their tonic pitch. The tonic would be all that matters to differentiate music, and because they can be transposed, all music could be analyzed the same, using functional harmony and Roman Numerals. It then would just take the liking of the author to choose a I chord over a i chord, with which to end a piece.

Is this a utopian view of music theory? Is it wrong somehow? Maybe scales are indeed useful to music theory, without which there’d be little coherence in melody. I don’t know. Perhaps if I were more knowledgeable, I wouldn’t be misguided as such.

Hi, it’s nice to see you thinking about old systems like the music theory, which originates from the ancient Greece!
I think the modes really have a function, because when you say: this song is in the Dorian mode, I know the song will sound peaceful (in my case, I assume everyone experiences the modes differently). In Phrygian mode, I know it will sound “Arabic” and intriguing. And so on.
On your example, these are two different things. In the VI - VII - I, the major I comes as a surprise, and it’s mostly used to end a song in minor (i) with the major chord, to make it finish in a happier way. This is called the picardian third (you’ll find some interesting Youtube videos on this).
In the bVI - bVII - I, the two first chords come as a surprise. The song seems to make a sudden switch to the minor key (i), and ends back in the major key. In the Pearl Jam song “Even Flow”, the chorus features bVI and bVII chords. So while in the first case, the I is the odd one, in the second case the bVI and bVII are abnormal and the I is the resolution.