You have it in piece-parts above. The answer to your original question is in two parts, both in your control:
1. How do you define and like bark? Crusty/hard carmelized, or softer more like meat texture?
I see where you prefer the crusty/hard carmelized bark. See, I dont. To me it's too much smoke on the outside and I prefer softer bark. It's ok, we just prefer
them differently. Doesn't mean I dont like bark; we just define what the perfect bark is rather differently.
2. How much smoke (and the quality of smoke) you have coming through to the meat on your smoker.
A good bit of billowy white smoke and you can have a very bitter blackened crust bark. Managing sweet blue and you end up with only as much smoke as you desire and a crusty bark.
Sounds like you probably want to focus on your smoke and stay away from the foil, and IF you use foil use it probably at the end to help the butt re-hydrate.