Ninja vs. Dragoon

[Sleigh]

Right...perhaps you misunderstand.

Storm's eye vs Storm's path - you lose mitigation
Storm's eye vs BB - you lose threat

So, regardless of how you look at it, one additional set will lose you either mitigation or threat, because of the opportunity cost of doing a second maim inside of the maim buff window. You can make the case that you don't need the threat, but the cost is there.

As OT you can always rotate SE > SP for minimal DPS loss (far less loss than a NIN has using Dancing Edge over Aeolian Edge), so there's no cost of any sorts attached in that scenario.

As MT you can coast off your opener's aggro depending on the turn and keep both up regardless, eventually. Unchained + Berserk aggro is simply too high. If you want to look at it as a scenario where you HAVE to keep up BB with a WAR MT, then NIN keeping up Dancing Edge is a relevant tool, but it's not very useful in practice.