Good catch. I will make these promotions for Vengeance discipline. My plan is to put stronger heroes on later techs. Os-Gabella should be one of the stronger heroes. Gilden is "just" another archer. These heroes might need balancing, though, both on their raw strength, their promotions/gears and their unique utility. IIRC, it is impossible to make promotion that allows units to climb mountain. I have to define this ability in UnitInfos. But giving late game Khazad unit this ability is fine, IMO. Maybe the Hornguard? Or the Myconids?