There are many operators, so your definition of cattle barge might come into play. Some operators take only small groups on small boats. Some take larger groups on larger boats. I guess we all want to avoid the large groups on small boats, and we all wish we could find small groups on large boats. Your tolerances must be the deciding factor.
While Red Sail does handle cruise ship traffic, they DO NOT put stay-over guests on a boat with cruise ship divers as a matter of course. They have to take the boat down to the harbour to pick up the cruise ship guests, and with widely varying cruise schedules, it's just not practical to combine the two.
In December, the expected winds may blow out some days on the North Wall. Ask your chosen operator about options for diving elsewhere should this happen.
While overall stay-over tourism has been down the past year post-Ivan, many locations report brisk bookings for the coming high season. To be certain of getting your preferred dates, I'd suggest booking with your chosen dive operator soon.