How did your wife get infected - does she work in healthcare or the service industry?
The evidence seems to suggest that natural immunity is limited... although there could be something to natural immunity *and* one of the mRna vaccines. Since you are not vaccinated and only have antibodies from Covid A from around December, most likely your natural protection has seriously waned (not to mention, may have very limited efficacy against COVID Delta). I though you lived in the South - Texas or Florida, right?
I've noticed that with COVID, unlike other viruses, people do seem to get sicker when they are exposed to larger concentrations of the virus. Other viruses, it doesn't seem to matter how much of the virus you're exposed to. If you recall, one of the doctors in Wuhan China that was one of the first persons to become "famous" by being infected with COVID... if you recall, he at least appeared to be a healthy, younger doctor. His hospital was besieged with COVID cases, so he was exposed to a very heavy viral load (I presume, since China covers everything up). He ended up dying. Btw, just google it, his name was Dr Li Wenliang. Also, as far as my comment on viruses, I was thinking about viruses such as the flu and chickenpox, for ex. Whether you get a heavy dose or small does, it doesn't seem to matter as much. At any rate, I did some googling on that Wuhan Doctor that China tried to cover up, because it always stuck out to me that so many people (like you and your family) had somewhat mild cases of COVID, while others have had much more severe cases. I wondered if Dr Li's viral load of COVID had something to do with his dying.
I ended up finding a NY Times article on the subject (see below). It does seem to confirm my suspicions... it is though Dr Li died of COVID (partially) due to the very high viral load he received from early exposure to large amounts of infected Wuhan patients:
I also remember reading an article about a vaccinated couple in their 60's that took a vacation to Mississippi (from IL). Well, MS is one of the worst states in the union for infection rates and transmission levels.... meaning, you have a better chance of not only getting infected, but receiving a larger viral load, as well. Well, Candace Ayers, 66, double vaccinated in March, died of COVID Delta in early September.