Yoshi's Island is a terrible, random, and uncompetitive stage.
Frigate Orpheon's randomness is heavily telegraphed randomness. The side platforms are tolerable because while random to a degree, they follow a pattern and for the most part CAN be relied upon by a player.
Pirate Ship's randomness is heavily telegraphed randomness.
Norfair's randomness the ENTIRE SCREEN SHAKES to let you know it's coming and the CAMERA ZOOMS out.
Yoshi's Island, with absolutely no warning and completely randomly, produces a platform that can effectively save or remove stocks and a completely random element with no warning that can cause obscure locks, interrupt certain recoveries (Ness, Captain Falcon, Ike being a few), and cause hitlag from moves, which unlike Melee actually matters in this game due to much higher hitlag.