Luke is great in raids. He can solo (as in, by himself) the rancor raid, is a part of an AAT solo team, and is needed for the Chex Mix team in the sith raid.
He’s also needed in territory battles, and works well in territory wars. And he can still work in arena, even though he’s not in the current meta. He does solid amounts of damage, counters, inflicts debuffs, and his most useful zeta spreads turn meter to allies even when he’s not the leader. He’s good to have in all areas of the game except fleet.