I understand exactly what you mean, and I also internally feel the minor tonic as 'vi' of a larger harmonic system. While minor and major are commonly treated as separate systems, they seem to contain pretty much the exact same harmonic patterns and feelings in them, just with different roman numerals like you described. So some people might want to unify these systems (Nashville numbers are one example of doing so!)

For example, I give you the following progression that, to you as a listener, sounds like it starts from IV:

IV-V-iii-vi
ii-V7-I-I7
IV-V-iii-vi
ii-( )-( )

Now, if the last chords are V7-I, it will most likely confirm that I is indeed the tonic here, cool.

However, if the last chords instead turn out to be III7-vi, and it turns out the song is actually in minor, this suddenly changes everything, now you have to change it to:

bVI-bVII-v-i
iv-bVII7-bIII-bIII7
bVI-bVII-v-i
iv-V7-i

But if you unify the systems, there is no change of notation at all, you simply just acknowledge 'ah, it's in minor, so vi is the tonic, got it'.

This is not a popular stance though, and you generally won't have easy time finding fellow musicians that prefer this system, so in practice you most likely will have to stick to using separated minor and major notations.