Are you taking in account the quest gathering speed?
PETLESS?
Their method is instant. You go out. Go back in.
SW you have to fly or wing back to town and get another quest.
For people who have no flying pets. Their Method wins hands down completely.
Including obtaining the quest, you'd only need to run around 1.5-1.7 Shadow Warriors to compete with Their Method. Seems possible seeing as how the mission takes 1/2 as long.
Using Goddess Wings to cut the travel time in half. If you're saying that's unnecessary spending, I think the increased use of SP pots in Their Method adds up to more.
Depends on the player I guess. Though as far as speed running goes, the fastest time in my old Guru thread was 3:27 for Shadow Warrior. Unless you're so bulky that you can 1-2 Windmill the zombies consistently, you'll have a really hard time clearing that in under 5 minutes on hard.