with regards to weather similarity
Coco Cay is actually Little Stirrup Cay of the Bahamas and 135 miles due east of Miami. It lies on the south east side of the 'Northwest Providence Channel' thru the northern Bahamas and is part of the Berry Islands.
Castaway Cay aka Gorda Cay of the Bahamas, lies on the northeast end of the NWP channel, 29 miles to the northeast of Coco Cay, making it about as far north as Fort Lauderdale, 160 miles away. Temperatures of both water and air are going to be almost identical
NWP Channel is deep water .... while the water to the other side of each island is 'shallow'. There is no high ground around to provide much wind protection. Cocoa Cay tender channel faces north and the Castaway pier south-southwest .... and bad wind at one has a pretty good chance of impacting the other . . . Disney has very little spare room at the pier and SOMETIMES can't safety get to the pier in a cross wind ... RCCL has issues with bouncing tenders for the ship holding position north of the island.
from perspectives of weather and sea conditions I rate them equal . .