Woah woah woah!
G&W is amazing on Pirate Ship. He's is quite broken on it, along with TL, Ness, and MK. I don't know why you would think G&W would be bad on that stage; he's pretty good at water camping using invincibility on his upB -> key.
Anyways, if you need a replacement on worst stages for G&W, try Luigi's Mansion as being one of the worse ones for him. Depending on how liberal a stage selection you're catering to, Mario Kart is probably G&W's worst stage overall, gaining nothing from it's flatness, and losing his amazing edgeguarding. Also, depending on the matchup, Battlefield can also be your best pick vs G&W; Snake, MK, Marth, etc all do very well here as their stage, but as this is a general outlook, we can ignore that.
With Bucket Braking, Japes just might not be that bad for G&W, but we havent covered it yet.
Game and Watch
Best: Rainbow Cruise, Corneria, Green Greens
Worst: Jungle Japes, Luigi's Mansion, Mario Circuit
Is probably how it should look.