Legion Exercise 4 is the most rewarding quest not the fastest, it's probably one of the most annoying quests to farm legion tokens. Just use the bots, and yes get the Soul Collector as soon as you can.
fastest way to get LT is the LEGION TOKENS (non soul collector)
it takes about 10mins to finish the quest if you use bot but when you farm it manually you can do the quest in just 3mins or less than.
hope this help