The vaccine is probably just ramping up the immune system response for a few months. That alone would prevent death and since we don't really have anything else, it's still better than nothing.
However, vaccination induces a slightly different immune response compared to natural infection [2][3] . These differences may account for variation in effectiveness between vaccine-induced and naturally acquired immunity.
[1] Rapid induction of antigen-specific CD4+ T cells is associated with coordinated humoral and cellular immune responses to SARS-CoV-2 mRNA vaccination https://www.cell.com/immunity/fulltext/S1074-7613(21)00308-3
[2] Antibodies elicited by mRNA-1273 vaccination bind more broadly to the receptor binding domain than do those from SARS-CoV-2 infection https://pubmed.ncbi.nlm.nih.gov/34103407/
[3] mRNA vaccination compared to infection elicits an IgG-predominant response with greater SARS-CoV-2 specificity and similar decrease in variant spike recognition https://www.medrxiv.org/content/medrxiv/early/2021/04/07/202...
What's the variation you are referring to?
It's all preliminary data. However, the sinopharm vaccine, which is the whole virus, not just spike protein, seems to lose effectiveness after several months as well.
I find that when people use "categorically" in an assertion (denial), then there's good reason for doubt.
1. https://www.forbes.com/sites/roberthart/2021/08/25/vaccine-p...