I just want to point out that GNB's LB is not "interruptable" other than by killing the GNB. If you are stunned, Silenced, Miracled, Charmed etc, then you will be unable to manually execute Terminal Trigger to finish it early, and you may not even be able to move around, but you will in fact continue to dervish and auto-execute Trigger at the end. Regardless of if the animation itself continues to play, the damage and effect will continue upon those in range. You may have been unable to Recouperate because you were still actually spinning even if the animation was no longer playing (the LB buff should remain).

The same goes for the similar DNC action "Honing Dance". These are easy enough to test via duels against WHMs or other jobs.

GNB's LB is incredibly strong for being a 1 min cooldown and especially when combined with Rough Divide for the movement and damage bonus. It's definitely balanced around the opponents being able to run away, guard, or knock the GNB away, and it's as certain a death as Sky Shatter if players don't get out of the way, especially because it's easy to instantly follow-up with a Double Down.

GNB definitely struggles with being focused more than other melee because much of its damage comes from oGCD actions that could otherwise be recuperates and it's lack of a good escape option. It's very much a 'hit em hard and fast' job that relies upon other jobs setting up controls to knock opponents down because it lacks any good control of its own. Its limit break stun isn't even exactly 'on demand' because of the 1 sec delay in being usable after beginning the Limit Break, prompting quick guards or avoidance from savvy players; so I favor using it when there's multiple targets to hit or move between, or when they "have to" pass me like many stage hazard events.