are you sure the 2-5-1 thing is not related to the cycle?
the cycle goes in this way: C G D A E B F#.. and so on
and the 2-5-1 progression is:
Dm G7 C
Am D7 G, and so on
the connection between all of them is that the ii is the relative minor of the previous key of the cycle (Em and G for example), and the V is the next one.