Round shot is more efficient than Fury since it is unlimited whereas one has to keep going to shore to get Fury... But Fury is still stronger. Yet still Round shot with all cannon passive skills makes it more efficient. Increasing Take Cover, Ramming Speed and Full Sail just increases its time. I wouldn't mind it for Take Cover but Ramming Speed puts u out of control for a while and when I out 4 on Full Sail I realized it would have done well with permanent Passive skills such as Windcatcher (speed), Tacking (turning), Taskmaster (reload), Treasure Sense (gold - not so needed now). But for mostly Grenade, Cannon, Pistol, Staff, Doll and Dagger Passive skills are the MOST IMPORTANT as it raises ur pirate's strength. As for the active skills only one or two should be maxed, such as, Voodoo Staff - Desolation or Flaming Skull; Dagger- Viper's Nest and the first one; Doll- Life Drain and Swarm; Grenade - Fire Bomb and the last BIG one.... Cutlass is an exception as every active skill is important. But some active skills that act in a passive way are very helpful - Brawl, Throw Dirt, etc. Grape Shot too, but it doesn't work now......
One note : Lightning is extremely important for long distance shots and mast crippling, slightly more effective than Fury....