Well after 4.f3 g4xBh4 5. f3 x Ne4 you have this strange position - black has the advantages of two bishops in a fairly open position, the open g file but the disadvantage of the weal, isolated and doubled h pawns. White has the strong e4-d4 pawn centre, and the doubled e pawns are interesting - giving greater central control and white may be able to use the open f file. It is approximately level, with chances for both sides to win if they play well. I think after the retreat, black has a minuscule edge.

But after 7... Qb6 8. Nd2 Qxb2 9. a3 Black simply plays Qxc3, which is horrible for White: the d4 pawn is now pinned against the rook, and nothing can safely defend it!

I think you can say that - certainly Fritz prefers d5 or maybe just a queen move. Sure Black can go a pawn up, but the extra, doubled d pawn doesn't mean much. After 10. e3? exd4! the Fritz evaluation moves from "slightly better for black" to "black's advantage is more than one pawn".