You are correct, I believe every single Caribbean destination will suffer to some degree. I have travelled to every island you mentioned above (including Cuba for over 3 months living in the homes of Cubans) and I will say hands down that Cuba is the most unique, diverse (not talking about politically) and interesting. There is so much to do and see outside of the typical beach and resort type vacation.
Its easy and safe to travel around the island, with various casa particulars that are very well marketed (and this will only improve if the embargo is lifted).
IMO Cubas unique culture and arts cannot be compared to any other Caribbean island, it is in a class unto itself!!!!!! This will be Cubas appeal, this will be its selling point! Cuba has some of the best artists in the world!
Niche travel is booming in the travel industry. Many tourists (especially those with money, are yearning for more than the typical resort vacation, waterfalls, snorkel, boat cruise, etc. things that you can do on any and every island....talk to the tour business owners in Playa Dorado how business has been on the decline over the years because how many times can you climb waterfalls and go on a safari truck tour before you get bored?). New and diverse is key. There is too much same, same, same on many Caribbean islands.
Many more tourists will want to be immersed in the local culture, exposed to the local arts and travel in a way that is unique and educational...and not just sit on the beach for their entire vacation.