All of the articles you are referring to are for acute/mild/moderate cases of COVID and do not cover to the significant number (particularly in younger cases) o

All of the articles you are referring to are for acute/mild/moderate cases of COVID and do not cover to the significant number (particularly in younger cases) of asymptomatic and still infectious carriers, which I specifically called out in both the first and second post. The whole point is that the adaptive immune system doesn't really ramp up for many days up to weeks, while viral load typically peaks at 3-5 days. That's why the second shot is typically delayed for the MRNA vaccines. A young asymptomatic carrier with a strong innate response who recovers early is unlikely to develop a significant adaptive immune response (e.g. test positive on an antibody serology) thus they are also then very unlikely to develop durable immunity.