In doing the alliance war campaign, and seeing the last part of tides of vengeance, something I feel needs to be said about this.
Shaw says the planned attack on dazar'alor was to destabilize the hordes relations with the zandalari in an effort to weaken the horde instead of gaining a new force to its side.
And while the alliance killed rastakhan and destroyed much of the zandalaris fleet, what they ended up doing was making the pack between the zandalari and horde stronger as a result.
Its not like the zandalari can't build more boats, and they now have another ruler to replace their one just killed, and in doing so kinda made it personal as a result.
So yeah, what did the alliance really gain from the attack again?