Cozumel might fit the bill. Lot's of restaurants. Diving and snorkeling plus whatever tours if you want.
Not sure why Grand Cayman is not on your list. Last time I was there (been awhile), there were plenty of good restaurants and decent diving. I am not sure if you can dive stingray city now. Though it is expensive on GC.
If you want more topside stuff then you have to choose somewhere that has a bigger population and tourism.
We just got a letter saying Sandals Emerald Bay, Little Exuma, Bahamas was converting to a Beaches starting Aug 15. We stayed there during a soft opening years ago and liked it. You might call them and check the opening date and what they offer (soft opening - hint). It was a Four Seasons hotel. We have not been to any of their properties lately but they are always nice and better food than Mexican AI.
The beach there is very good but not much snorkeling - it is mostly sand.
The diving is not bad but I would not say world class. I did dive a little blue hole there with an outside dive op. I doubt Sandals would take their divers into it.
We most always dived with an outside dive op. If you search SB there are plenty of discussions on Sandals diving. Their dive operation is not bad, it is professional but highly structured.
You could try Nassau Bahamas but I was not impressed overall with the diving. On the other hand, lots of sharks. The Bond wrecks are were becoming piles of rubble. More so by now no doubt.
Other places I have been to have smaller populations and we were farther from towns so less to do other than dive - which was the point really.
