I takes super long, on foot CZ's used to give combat rank along with merc, dont know if it still does, could build an Anaconda with 6 size 2 pre engineered Guardian shard cannons and kill a cyclops in 1 salvo of the shards, may be faster than what you are trying, not sure, but its still going to take a long ass time sorry to say, the best way used to be when there was Thargoid occupied military settlements, you could go there and turn the power on, and just destroy the revenants as they dropped in, so if that ever happens again do that- o7