Yup I have upgraded my Storm Boltor dmg barrel, upgrades with the 20% ranged dmg perk + reliability and ammo capacity for my Chaplain. Yep I feel the Boltor is quite underwhelming.
The Redemption stats are quite misleading, since it shoots pellets its shot deals a lot of damage and can 1 shot most enemies, far more effective in most situations on the cramped space hulk. I'm also not sure about this but it seems the pellets also penetrate through multiple enemies which adds even further to its value in clearing hordes.
On the topic of other weapons which the boltor competes against: I think the Spear of Caliban far out performs the boltor, there is the feature on the SoC aiming reticle which adjusts to the enemies head if it is within the circle. However I guess it can be argued that the weapon is really suitable for when friendly fire is off.