They cheated—true.
But—the more interesting and nuanced question is exactly how steroids helped them break the record.
Can those drugs help you hit a curveball?
I have heard that argument from the steroid apologists.
Where to start:
Look at their numbers before and after they admitted to starting use. So, they just went on a tear (at an age when most players decline) as a coincidence?
Strength helps such that when you hit a ball, which under normal conditions would have been a fly ball out, it now suddenly flies over the fence.
It helps that when you normally would have gotten tired or worn out during the long season, you are healing up just fine and can continue along your merry way.
If the players weren’t sure it helped, then why the secrecy? Why Balco?
One may as well ask, has it been proven that steroids and blood doping helped Lance Armstrong? Different sports for sure, but different doping too.
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.