HOFi Giac's upcoming Lairiable branches are Spider and Shoals, and the only rPois is a fragile +8 mace. That's a great example of why HOFi goes Ely first. Spider is easy with Ely's Purify and Heal Other. Meanwhile Beogh struggles in Water and Poison.
The first branch that NOT worshipping Beogh counters is Orc, since the convert option is a panic button. The first branch that worshipping Beogh counters is Elf. Smite melts elves, as does stairdance ambush or swarming.
Elf is the inverse of Vaults. Elf magically challenges resistances with less physical damage and low AC and HP and SH, whereas Vaults' theme is high physical damage and physical defenses.
In both branches, Smite preserves mobility by removing fixing monsters, a key to survival. Mobility permits safe positioning, allowing followers to supplement player damage.
In other words, orc's natural enemies are elves and humans, and they're good at killing both.
Depths is a continuation of Dungeon, and neither favorable nor disfavorable to Beogh. The increase of one-to-many monster attacks starts diminishing follower effectiveness, but follower leveling can keep pace. If nothing else, orcs make a beefy low-EV sacrificial rearguard. Since HOFi will abandon Beogh for Zin soon after finding the Abyss entrance, followers are expendable by this point. A faith amulet helps keep Beogh viable until its time for the grand finale at Vaults:5, with an optional curtain call sniping Geryon in Vestibule.
Orcs don't have a long lifespan. Orcish invasions are supposed to be nasty, brutish and short. Inevitably they run up against something that refutes their delusions of racial supremacy. Whether the total failure to learn from this repeated lesson is due more to a lack of survivors or intelligence is a question best left to the embedded cultural anthropologist, who typically winds up in the pot.