I totally get that, and I am not trying to say someone is wrong in saying they sound similar. But to me, there's no controversy here. That's my point. I get that they can sound very similar, but that means that it's very easy to plagiarize something. Just use the same structure and change the melody around.
"where the tonic is always i or I"? The tonic is the i/I by definition. You can't say "the tonic is vi here". That would be tonicization, and that would be a different tool. When you start a harmonic analysis, the first thing you do is figure out what the tonic is. When someone's harmonically analyzed the FF song in question and set it as a major scale, they would have a really hard time to explain the III that occurs, as opposed to the iii that should be there. In a minor chord, it's so commonplace to borrow the parallel five that it's practically impossible to find a song in a minor key that uses the "vanilla" v instead of a V. It creates so much more to use V.
No see, you say "in terms of actual music theory" in response to my post. That either means that you say what I say isn't "actual music theory", or you didn't get that far in my post to see that I do some 'actual music theory'. I didn't want to assume you were a douche by somehow saying what I wrote wasn't actual theory, so I asked if you didn't read what I wrote, since I very specifically touched on exactly the same things.
See, the main issue I have with what you're saying is that you're saying "it doesn't really matter if it's a minor or a major key, since they're relative". That they both have the same notes, and as such, "they have the same chords". Yes, they have the same chords, but their harmonic function is so hugely different, and it's a big part of harmonic analysis to understand the harmonic functions of each chord. So when you start by saying "this song starts with a vi", that would mean we start in a way where the tonic isn't established. There are many awesome songs that start on a ii, which means your mind start by figuring the first chord is the tonic, but suddenly it throws a IV at you instead of a iv, and then suddenly your mind figures "oh, the tonic isn't the starting tone". The chord progression of a minor key works differently from a major key. In either, you always want to resolve back to the i/I. It is the most stable part, where the song can be at rest. It can build tension from there. As such, the harmonic analysis of the chord progression as a major chord is flawed, since it can't answer what the harmonic function of each chord is. That's because the tonic hasn't been properly labeled.
These are nuanced topics on the area, but it really separates the field. After all, try googling what chords are in a minor scale, and you'll find poorly written pages where people claim it's the same chords as in the relative major. It's impossible to find someone that doesn't have a degree in music that gets how integral the V of the minor chord is..
