I read this note from the developers:
https://www.blackdesertonline.com/news/view/4964

It's very welcoming to hear that Pearl Abyss is working to ensure the actual effects applied match their item descriptions. There has been an issue for a very long time is the Blue-grade ship cannons PVP damage does not apply apply properly. This has been tested in that PVP damage is capped on both Carrack: Valor and Carrack: Volante blue grade cannons. +10 level Blue-grade cannons do the same PVP damage as lower enhancement levels. Will this be fixed by either fixing effects applied or the changing the description of the equipment?

I think they should fix the tooltip instead of fixing the damage. That isn't a bug but more of a damage cap

Now imagine +10 blue cannon valor is fighting +10 blue cannon balance, advance, or even volante. None of them will have any power to fight back at all if the displayed damage is what they deal

Boat pvp imo is one of the more balanced and zero rng dependant unlike land. Its really heavy on positioning, knowing enemy tactics, and faking movements. Making valor cannon damage into the true number will make valor absolute BIS simply because they can just trade shots and win. Right now volante have sacrificed cannon cd for extra speed. If the damage tooltip is fixed, balance and advance winning chance is getting even lower and volante is gonna be dying breed simply because less than 3 percent marginal speed increase cant compensate a 40 percent firepower gap anymore