Bacon Bits
Legend
So ... is the general thought that Disadvantage would make it too good against low AC opponents and better against high AC opponents? That it would be about equal at the medium ACs, but that's not where it's a problem?
My thought was to avoid stacking -5 to hit and Advantage. Would that not help rein it in?
Same goes for Sharp Shooter.
The problem is that means you just always use it when you have disadvantage. It's the problem of only allowing one penalty at a time and then introducing a mechanic that applies a penalty for a bonus. It means that whenever you have the penalty, you'd always use it.
The easiest change is to make the feat -5/+7. That actually makes it almost always a bad idea to use, but I'm still not a huge fan because it still says you have to do algebra at the table and it's hard to see that the math goes against you so quickly.
If I were going to leave it as intact as I possibly could, I would do this:
Before you make a melee attack with a heavy weapon that you are proficient with, you may choose to make a mighty but reckless swing. Make your attack roll as normal. However, the attack also has a 50% chance to miss unless the target is incapacitated. If the attack hits, you add +10 to the attack’s damage.
That adds more dice rolling (boo!) but it doesn't have problems with going off the die with bless and other attack bonuses, benefiting from advantage, etc. Sure, someone with a Blowgun is still always going to use it, but once your average damage is 10 it's actually not worth it anymore. The ability becomes a complete gamble, especially once you get bonuses to damage rolls. The math means that the worse you are at attacking, the better it is to use this ability. The more skilled you are, the less benefit you get from it.