DDD isn't much of a threat on Onett. He still loses to his counters here, or at least the walls wouldn't be a problem at all for a lot of the cast.
Pirate Ship was always considered a legal stage on the BBR list, but people just didn't know much about the stage. The rudder camping thing before it was found out to not be that good caused the stage to be unused in tournaments sometime in 2009.
You get offstage damage from rudder camping as well as risk dying, and 2/3 transformations makes you leave the transformation, and you're vulnerable when resurfacing. Rudder camping is not very viable as a tactic. The water is WAY too laggy to be able to be camped effectively. Only like 2-3 characters can do much, and that's still worse than their offstage games on other stages.