I doubt SS was the problem here
If the fighter is dealing 100 damage per turn, only a portion of that is from sharpshooter. Best case if they are level 20 making 4 attacks per turn, and their hit bonus is equal to the enemy's AC, they get 40 of that 100 damage from sharpshooter.
Yes, it strong against weak enemies - eg a level 10 fighter with archery fighting style attacking a goblin would be hitting 75% of the time so would be dealing an extra ~3 damage. But killing lots of weak enemies is a niche.
However, as the enemy AC increases and so does, the fighter's damage, the decreases. The feature becomes weaker and weaker.
A quick comparison:
- Early game: A fighter with 5 average damage and +5 to hit vs a target with 15 AC: 2.5 damage on average, 4.5 damage with sharpshooter (equivalent to 2 damage bonus)
- Mid game: A fighter with 10 average damage and +10 to hit vs a target with 15 AC: 8 damage on average, 11 damage on average using sharpshooter. (equivalent to 3 damage bonus)
- End game: A fighter with 20 average damage, +15 to hit vs a target with 20 AC: 16 damage on average, 16.5 damage with sharpshooter (equivalent to .5 damage bonus)
I would recommend you do similar analysis using the fighter's character sheet. Calculate their damage with and without compared to several enemies that you would fight at that level. Every analysis I've seen comes to the same conclusion; "+10 is a big number, but in actual play the feat is situational" - it's notorious for being a trap for newbies.
The feat is good, but only when used in conjunction with boosting your to hit (eg adv from hiding).