The answer depends a lot on your personal enjoyments-art, architecture, beach resorts, local food, etc. Another way to say that is that Pompeii was on my "life list", and I was very glad to spend almost 8 hours there. But it is desperately exposed to the heat and sun, and a challenge to walk safely on worn stones even for the well-abled. The Naples museum is, after all, a museum, and some people find them sterile. BTW, I thought the Farnese Marbles were almost as worth the visit as the works moved (for protection) from Pompeii.
I also really wanted to see Positano (but had no real desire to sleep there.) My personal opinion is that Capri is a much nicer pedestrian experience among the international clothing and jewelry boutiques that I would never actually buy anything in. But an hour or two to view Positano is appropriate. Having visited Amalfi and Ravello on foot as well, I liked Ravello the best, but it is too out of the way unless you hire a car and driver for your limited time on-the-ground. I'm saying that Positano alone is sufficient. (OPINION!)
Naples is often disdained, but I agree about its cultural and historic importance. But I put Pompeii and the AC ahead of it for your schedule. BTW, we had to wait an hour outside in the heat to get a table for Naples pizza. And it was superb, but a bit damp for American tastes. You do need to plan (post Covid) for possible fierce crowding at the end of July, anywhere on this vacation. I would make the most of Capri mornings and evenings. Have you checked on the best way to get your luggage to your AirBnB (which I disapprove of, anywhere )? Much of Capri is fully pedestrianized.
