It is a strong feat but it not nearly +10 damge in actual play.From actual playtests, I can tell you Sharpshooter is ridiculously OP. Maybe not by itself, but when combined with Archery Style, Bless, etc, it's basically a +10 boost to damage. You have an effective +4.5 to hit over the norm - which basically counters the -5, and you never have to worry about cover, so there goes any tactical limitations, as you're now effectively armed with a lazer accurate machine gun that can shoot across any classic D&D encounter map.
The -5 is actually a -6 because and the bonus damage is +9, not +10 because you traded an ASI for it that would have boosted both attack and damage by 1. The long range and cover bonuses are bigger benifits than the damage boost IME.
Comparing a 16 Dex with archery style with SS to an 18 Dex archer without SS the damage difference per attack is only 1 point against a 16 AC target and you have a worse dex save and worse skills. That damage difference increases at lower AC and decreases at higher AC. At AC19 and above the guy who did not take SS is going to do more damage. That of course assumes you have no cover and are not at long range.
That also assumes you have no damage riders. If you are running hunters mark or hex or have riders like Sneak Attack or Dreadful Strikes it will fall behind someone who took the ASI at a lower AC.