I'm not a metallurgist, nor do I play one on TV, but I think if there were a better option for bullet jackets, we'd see it already.
When smokeless powder came out over $100 years ago, people learned that they needed to put some kind of jacket over their lead bullets, as solid lead wouldn't hold together without a jacket of some sort (in the new rifles with faster bullets and tighter twists). First, they tried solid copper, but that lead to excessive bore fouling. Militaries and ammo makers eventually settled on gilding metal (a brass with ~5% zinc) as a harder material that didn't foul as bad. Given that zinc is cheaper than copper, I'd think that manufacturers would want to maximize it's use in bullet construction.
Ergo it's reasonable to surmise that if a brass with more zinc in it (or some other cheap element) were excellent for bullet jackets, we'd see it.