Your tools, in BS, at a disadvantage are:
2A, 6B6B, 2A+B, Throws, 9KB, 4B, B+K, and sidestep -> 22B.
I'm talking about small disadvantages here (-2 to -4), not moderate ones (-9) - the game here starts with 6B6B, which is fast (i15) and guarantees a nice chunk of damage. Importantly, it's fast enough that its generally precludes an opponent using good, slow tracking moves. Once you've limited the opponent to fast moves...
2A beats almost anything they do that isn't a 2A (Voldo's BS 2A is excellent, barring range issues)
4B and 9KB beat lows - if they do a slow-ish low, 4B gets a counterhit and you get a nice chunk of damage.
B+K thumps opponent's 2As, and throws will get around an awful lot of stuff, particularly if the move does not track well to their left.
Finally, 22B guarantees 104 damage on a normal hit if you have meter. Simply sidestepping if you smell a B,B and hitting with this move is pretty fantastic risk-reward for you.
-Cross (Edit: Should note that didn't really include 2A+B. It's a risky move to do at a disadvantage. It isn't fast, if it doesn't evade, you're getting CH'd. And good players, faced with the above mix-up, will frequently just block. And then spot-block the 2A+B, and punish with whatever the eff they want, because you're at -22ish)