MLB didn't formally ban steroids until 2005. So their use through the 2004 season -- which covers the heyday of the Bash Brothers -- wasn't 'cheating.'
Steroids don't help questionable hitters hit a curve ball but they do help with recovery from a hard day's batting practice. You can practice longer and harder without it wearing you out, which gives the marginal batter a better opportunity to "up" his game.
And if you started a out good batter, some of your shots that would have died out at the warning track become gopher balls.
It's clear from Bond's track record that he was a much better homerun hitter after steroids than before. That is beyond dispute.
I believe human growth hormones (HGH) had a much bigger impact on baseball than steroids. I had seen reports indicating that they no only improve strength, but can enhance vision and hand-eye coordination. That would explain why Jason Giambi lost 65 points off his batting average and led the AL in strikeouts the year in the early 2000s when he showed up for spring training looking like an emaciated waif compared to his prior build.