Yes, primarily, but Torrent of Flame and MIG/INT bonuses are very nice too. Maybe Girdle of Mortal Protection is better overall, I haven't got it yet, but Cannoneer's belt is, at least, useful and fun option, I think
Anyone tried https://pillarsofeternity.gamepedia.com/Belt_of_the_Royal_Deadfire_Cannoneer with this build? I'm level 5th on POTD Solo now - IT'S INSANE!!!