TL; DR: It would shift the focus from good builds to good skills, sure, but it would only worsen the underlying problem.
While this change would reward skilled playing more and luck less, it would still be worse, in my opinion. High-crit characters like Bounty Hunter would certainly be somewhat inconvenienced, but it’s not like he needs extra ammo generation when played well. This would mostly force the Talent pick on level 15 to not spending ammo, and it’s already pretty much the most useful. The careers with lesser crit chance, i. e. practically all of them, would just lose Scrounger altogether, as it now would barely help sustain their ammo. Headshots, on the other hand, can be scored consistently with most ranged weapons, and they already give Huntsman a good capability for redeeming ammo, and actually collecting extra. Giving two ammo on each headshot to everyone would give everyone the capability to generate more ammo on every shot, thus making ammo drops even more trivial than they are now. Only a few weapons would not be affected. As a specific example, all of Kerillian’s bows are very accurate, and she should already be scoring headshots constantly. Gaining extra ammo from them would render Waystalker’s ammo regen Talents and Shade’s Bloodfletcher nearly worthless, and give Handmaiden effectively infinite ammo too.
As a side effect, it would likely slow down the pace of the game too, as people would stop to aim for headshots to redeem ammo, instead of shooting on the run or meleeing more.