The discussion on that post seems to support the grandparent, not you. Also, the article it's talking about says

> The new evidence shows that protective antibodies generated in response to an mRNA vaccine will target a broader range of SARS-CoV-2 variants carrying “single letter” changes in a key portion of their spike protein compared to antibodies acquired from an infection.

I.e. the current vaccines are not laser-focused, but are in fact less focused than a natural infection response, meaning they're better at covering against variants.

The most charitable read I can think of for your comments is that you're taking "immunity" to mean only the absolute you-cannot-catch-this-at-all level. Whereas the vaccines (and natural immunity) work far more on a gradient -- your immune system is primed to fight the disease off, and so your outcome at every stage is better than it would otherwise have been.

Note that the article was talking about the spike protein. I believe natural immunity also can target parts of SARS-CoV-19 that are not part of the spike protein.

In that sense vaccines are more focused, but the focus is on a part of the virus that is critical for getting into cells. There are limits to how far the spike protein can mutate and still do its job and the vaccine immunity covers a large part of that space.

> Note that the article was talking about the spike protein. I believe natural immunity also can target parts of SARS-CoV-19 that are not part of the spike protein.

This is my understanding as well.

Vaccine-derived immunity is more broad with respect to potential mutation of the spike protein/"receptor binding domain". Natural immunity is more broad with respect to the entire virus, as antibodies target areas other than the spike protein itself.

I believe that antibodies specific to the spike protein more significantly reduce the chance of initial infection, while antibodies specific to other areas of the virus are more effective at reducing the chance of developing symptoms.

It seems plausible, and I speak here as someone with no medical expertise whatsoever, that a vaccine-immunity that targets the spike protein and slows infection would still be pretty good at reducing symptoms as it would presumably slow the virus spreading inside you, giving your immune system a better chance to pick up on a specific-strain response before it's completely overwhelmed.

Given that there really does seem to be better outcomes for vaccinated people even when they have breakthrough infections, compared to completely-unvaccinated first-time-COVID-havers, there certainly seems to be something like that helping out.