Reasoning: All explorer pirates (excluding/including Jett, depending on how you look at it), use Nautilus Strike and I don't see why it can't be a skill all pirate explorers can access. The damage can be reduced to better suit a shared skill rather than a class-specific skill and Corsair can get a new 5th job skill that is equally as good as Nautilus Assault. It would be nice to have a skill for Corsair that summons all of their summons and gains all of all aboard's passive effects at once, or maybe an after image skill that mimics your attacks the way Night Walker's shadow partner does. I personally think a skill that activates passively would be better than having to press another key because Corsair already has so much on their plate to use, like Paragoteering, headshot, rapid fire, keeping up with 30 second duration summons, quickshot, etc. that need to be pressed at the right moment to deal the max possible DPS for their kit. Corsair is a class that needs quick hands to manage and I love it but there's starting to be way too many skills corsair needs to use because of 5th job skills being a thing. TL;Note: I like this skill as a corsair main but I think this skill suits all explorer Pirate classes since all skills do, in fact, use Nautilus Strike. I want to make it clear that I don't mind having the skill be restricted only to corsair and would like the skill to be limited had it had a different texture that resembles skills that only Corsair knows, like a giant version of Broadside.

So the skills that could replace it as Corsair's new V 3 skill could be something like/or:
Crew Rally: Summons the support of all your crew members at once and allows Kyrin, Captain of the Nautilus, to be summoned.
Level 1: 180 second duration. Summons all 4 crew members and gains all their buffs at once, while active, using Broadside now summons 2 crew mates at once and shares the cooldown/duration of broadside. Kyrin summon: Deals 750% damage 3 times occasionally to up to 8 targets. Kyrin Summon Passive: Reduces cooldown of non 5th job skills and non hyper skills by 17.5%. Cooldown: 360 seconds.
Level 25: 180 second duration. Everything stays the same aside from Kyrin's summon duration and passive buff: Deals 1350% damage 3 times occasionally to 10 targets and reduces the cooldown of non 5th job skills and non hyper skills by 30%.

Heart of the Sea: Manifest your love for the ocean as a physical entity, that mimics your attacks (excluding final attacks and Majestic Presence (which is a final attack?).

Level 1:Duration: 31 seconds. Deals 36% of damage done as additional Final Damage, when mimicking the Rapid Fire or Bullet Party skill, only mimics every other shot. Cooldown 179 seconds.
Level 25: Duration: 45 seconds. Deals 60% damage done as additional Final Damage, when mimicking the Rapid Fire or Bullet Party skill, only mimics every other shot. Cooldown: 140 seconds.

Nautilus Assault reduced damage to fit all classes would pretty much reduce the damage to half, especially for corsair because they would receive a new skill in compensation for the skill becoming shared with the other explorer pirates, and they can't have both until the next round of 5th job skills come about (if that ever happens).