So I will say one thing I don't think double gunning is an issue but I don't like the changes they've made to make double gunning excel over the years....
The sword combat was a lot better in the early years of the game compared to now. The weapon definitely has become outclass with everything else being better than using a sword
Swords can simply be walked away from anymore and the weapon has slow time to kill... infact if someone is trying to beat you with a sword you can hotswap double gun them before the sword can kill you which I do find to be a bit silly considering it makes doublegun better to use in close quarters than a sword
Blow darts are good for strategic play and hitting enemies from around corners with explosive darts and staying out of line of sight of those pesky guns which I recommend doing against double gunners by using g your environment to hide from them and nailing them when you can
Throwing knives can out dps double gun of you're good with it but a pistol snipe gunner will out range you if they are good and I do think throwing knives are a good counter for double gunners on deck combat
Overall I would say learn to get away from the sword till it gets a rebalance to combat and use the other weapons.