Sure that study has some good indicators, but there are a few limitations:
*It shows immunity lasts for at least 7 months, that doesn’t mean immunity is permanent.
*Of the people studied, a quarter of those who had been infected did not produce the long lasting immune response.
*The long lasting response may have been conveyed by multiple exposures. Similar to a booster shot, at the height of the pandemic many people were exposed to Covid multiple times. As the pandemic fades this will be less common.
At core we have good hints at long lasting natural immunity, but until time has passed we can’t know just how long lasting and how universal that immunity will be.
I think your reading comprehension is compromised, or that you are biased.
You seem to have missed the money line from the Publication.
“ Overall, our results indicate that mild infection with SARS-CoV-2 induces robust antigen-specific, long-lived humoral immune memory in humans.”
How could you miss that???