you're forgetting that we're resource confined, yes it looks awesome in theory but it wont get you more than 8 instant pyros, possibly 9 within a combust and thats stretching it. the pyro and DB legendary are generally better over all, simply bcoz they dont need the fights to be a certain length or require your guild to essentially not get gear in order to not kill bosses faster, benefitting you equally as time goes on no matter the length of the fight or the gear your guild have.
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aye, at which point its most likely going to be better to use the DB legendary over the TW ring.