I notice this kind of progression a lot, but I’ve always been stumped on how to best analyze it. Say that you have a song with a repeating progression A-G-F-D-C-A (all maj chords). Would it best be in the key of Amaj as I-bVII-bVI-IV-bIII-I? Or would we assume it’s in amin with a picardy third tonic, as I-VII-VI-IV-III-I?
For instance, Madeon - Finale is analyzed as being in minor, with a borrowed major tonic. There’s also 2 different analyses of Deadmau5/Kaskade - I Remember that highlight this confusion: http://www.hooktheory.com/theorytab/view/deadmau5/i-remember and http://www.hooktheory.com/theorytab/view/deadmau5-and-kaskade/i-remember.