Is there any reason that the Lightning Claws aren't included in the effects of Ancient Warrior?

Whatever the reason, I imagine it is the same reason that reaper autocannons that were in heavy use by marines in the great crusade and heresey aren't. Infact the only heavy weapon that is included is the heavy bolter, despite ALL of them, in thier descriptions, saying that marines are thier most common users.

It's most likely due to balancing factors. It's rare for a legion weapon, more so than power swords, and power fists aren't included in it either due to similar reasons I imagine.

Power Fists are included though.