> A subsidy of popular music by indie fans

That's an interesting problem — this is only true if indie fans listen to less music than pop fans.

Imagine there are 10 users, 9 of whom only listen to pop, one only listens to indy, all of whom pay 10$. Now consider two scenarios: A. everybody listens to 100 tracks per month, or B. pop listeners stream 110 tracks per month, and the indy listener streams 10 track per month

Scenario A:

    9 pop *  100 tracks =  900 tracks streamed
    1 indy * 100 tracks =  100 tracks streamed
    total                 1000 tracks streamed

    total to pop artists  = 900/1000 * 100$ = 90$
    total to indy artists = 100/1000 * 100$ = 10$

Scenario B:

    9 pop *  110 tracks =  990 tracks streamed
    1 indy *  10 tracks =   10 tracks streamed
    total                 1000 tracks streamed

    total to pop artists  = 990/1000 * 100$ = 99$
    total to indy artists =  10/1000 * 100$ =  1$

The argument remains that you'd expect your money to go to the artists you listen to, but the payment arrangements don't necessarily benefit mainstream artists over indies, unless indie fans listen to less music than mainstream music fans.

EDIT: Now that I think of it, it probably benefits pop music over metal and progressive rock (or, worse still, classical music), because pop tends towards short songs, so more tracks played over the same period of time.