One issue, Taking sharpshooter. Low ground gives at most a -2 to hit where sharpshooter gives a -5, so Add 10 to damage with a -15% to hit overall (loss of low ground penalty) if you are low ground. Equal ground it's a straight -25% to hit for the +10 damage. At lower levels this is Bad, as in Really Really BAD.
Vs say putting your first feat into ASI you can easily get an additional +1 to both Damage and Hit. Bow's are finesse weapons so dex based for both to hit and damage. Comparison of the two and simple number crunching says the ASI does more for you simply because you WILL hit more often. For any archer build your going to want at least 2 feats (1 ASI, 1 sharpshooter) so any build for a Ranger Gloom Stalker or Rogue Assassin or even a multiclass requires at least 4 levels in a second class or 8 as a Ranger. That does leave 4 levels to play with so your basic build is totally viable. But Sharpshooter at lv4 is unwise, ASI at 4th lv feat, the question comes then do you go for your rogue levels or get a 5th Ranger for the extra attack (IMO 5th in ranger) If you go 5th in ranger you delay the sneak attack/assassinate til 8th vs 7th (a trade off I'm willing to make)
What I'm NOT willing to make is trade of -25% hit chance and 10 damage For The +1 to hit and Damage. At Mid levels (5-9) that -5 to hit can really bite you in the arse, enemy's start to get better AC's at that time. Hence making it even worse than just the basic number crunching does. I really don't know of a boss at mid levels where I'd rather have the damage over the to hit. Where your run of the mill mobs might fall easier at mid levels if you hit (and that can be a big IF even with karmic dice) with Sharpshooter, the consistent damage from a better chance to hit usually serves you better.
Simply put ASI should always be your FIRST feat for almost any class. At mid levels you'll need the bonus to your to hit over the damage bonus. What good is that +10 to damage when your to hit chance takes a -5. Sharpshooter with your standard Archery Ranger setup brings you down to a +2 to hit in most instances, vs the +8 you'll pull with a 19 dex. Even if I have low ground penalties I'm still looking at a +6 to hit which means I'll hit more often even with low ground than with Sharpshooter as my first feat. If I only get a 5 to 1 improvement in hit's it serves me better in the long run on damage. Because you not only loose that bonus of 10 damage, you loose ALL damage if you miss. The best burst damage build will almost always loose out over a consistent damage build with a -25% fudge factor built in like Sharpshooter gives you. Once you get to higher levels and get some decent gear Sharpshooter is required IMO, but NOT UNTIL THEN. Without the gear and levels a -25% hit chance at low levels is just bad even with the added damage.
Sharpshooter at level 4 is fine, you just need to turn it off occasionally.
Just do the math with your average damage multiplied by your accuracy and compare with and without sharpshooter. I find that 40% and above chance with sharpshooter is better than 65% without. If you can obtain advantage or get to high ground it gets even better for sharpshooter.
Its just stupidly powerful, and if you dual wield hand crossbows its just broken. Don't ask me how you reload any crossbow that fast let alone two single handed ones. That was one great thing about Pillars of Eternity and their firearms, you had one hell'uva alpha strike but you were swapping to something else afterwards.
