Destiny mounted laser and Archangel rocket launcher have perfect accuracy. This doesn’t change with non-proficient use. The only downside is that snipers can’t use Quick shot on non-proficient weapons.
This doesn’t seem like it was intended, but then again Archangel is very high up the tech tree and would see much less use otherwise (ancient sniper rifle does similar job better in every way except accuracy).
Archangel is a very confusing weapon to begin with - it looks like a rocket launcher, but functionally is a low damage pin-point sniper rifle for non-snipers (it has no blast radius).
