If the old captcha helped wetsuit catch bots, maybe he should enable it again! he could ban hell a lot of accounts again. he probably can't get rid of bots completely, but he could catch them and ban from time to time.
I think it was the act of switching it that helped rather than which captcha it is. By changing it he caught them submitting responses to the wrong type of captcha. I suppose after he did that they just wrote a script to detect which one it is using. That's the problem, it's a game of cat and mouse.