Agreed. My solution was simpler, but just as effective. It doubles the short range and reduces the cover bonus by 2. So while a sharpshooter could make a 300 ft shot with a longbow against a target behind an arrowslit, they'd have -3 before modifiers (fighting style would reduce this to -1, but extra damage would make it -6). Just as with Great Weapon Master, I don't have an issue with the -5/+10, I just wish there were more fighting styles that could get abilities on par with it (Shield Master is iffy, Two Weapon Master sucks, and there's no Dueling Master)In all honesty the most broken part of sharpshooter is not the extra damage bit, it's that:
1) You can combine the part about ignoring cover WITH the fighting style (it's what makes the damage bit too strong)
2) You can combine all the elements of the feat, i.e. a 4th level archer can fire at a castle guard hiding behind an arrow slit of a castle tower (which normally has +5 AC) from 300ft away with NO penalty, except for a -3 (assuming they have the archery fighting style) for the 10 extra damage. It's really only this fringe case that is absurd.
In the past I've ruled the following:
1) You pick ONE of the options each time you fire an arrow, i.e. ignoring cover OR ignoring the range penalty OR doing the extra damage. Not all three.
1.a) The other option here is ruling that Archery Fighting Style instead "Ignores half cover with ranged attacks". It's the reason why the fighting style is +2 to attach as it's intended to counter the +2 cover bonus for firing into melee regularly and frankly is what the fighting style SHOULD have been in the first place. It also means the feat no longer stacks to reduce the penalty.