Well they did almost kill Tobirama and you know of the threads that were posted. Out of all the top strongest shinobi lists they weren't listed at all. (At least from what I've seen) Ay said they were terrifying despite his bravery and power. Darui got lucky by using his second most used word more than his first at the last second. They are said to be the descendants of the sage and possess the ninetails chakra and wield the treasures. I personally think they should be in the top 20 list at around 15 or something..