Someone who's known if the Harding Line 21 .. Rb8 is busted?

(1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. 0-0 Be7 6. Re1 b5 7. Bb3 0-0
8. c3 d5 9. exd5 Nxd5 10. Nxe5 Nxe5 11. Rxe5 c6 12. d4 Bd6 13. Re1 Qh4 
14. g3 Qh3 15. Be3 Bg4 16. Qd3 Rae8 17. Nd2 Re6 18. a4 bxa4 19. Rxa4 f5 20. Qf1 Qh5 21. f4 Rb8).

Now I recall that 22 Rxa6! (instead of 22. Qg2) was proposed as a bust to 21 ... Rb8. The point is that it should be bad to take on b2. Instead the silly 22 ... Rbe8 has been played and black has suffered after 23. Qb5. But if black is gonna play Re8 he better play it at move 21 (The Nunn Line). At last time I have grown skeptical about this "bust". The penalty after 22 ... Rxb2 is supposed to be something with c4 and if bxc4 Nxc4 with big advantage to white, but I think the Rook on the second rank is quite active. Someone who knows please?