First, those claims are speculative as they admit. Second, you cannot generalize from one or two small studies; for instance, other studies (the much-touted Israeli study) have found that natural immunity actually provides much greater protection.

We'll only figure out the truth long after it matters, so the question being debated is the risk of complications from the vaccine compared to the risk of complications from COVID. Given younger populations have very, very low risk from COVID, this is a subtle and complicated question to answer.