"Valid"? As opposed to "invalid music"?
> As you’d expect, the tonic I is the most commonly-used chord in the Rolling Stone corpus.
If it wouldn't be the most used, would it be used as point of reference and called the tonic?
> Rock uses plenty of V-I, but it uses even more IV-I. And the third most common pre-tonic chord in rock is not ii, like you’d expect if you went to music school; it’s bVII, reflecting rock musicians’ love of Mixolydian mode.
I-V and IV-V seems to be the same with the point of reference moved to IV. And IV-bVII-V is I-IV-V.
Is a fixed point of reference really needed? Doesn't it just add unnecessary complexity?