That isn't quite true. Since sars-covid-2 is new, it follows of course the specific vaccine is new. The RNA/mRNA approach goes back 30 years to HIV research, and the current vaccine has many years of research (directly from SARS-1 and MERS, and possible mitigations). A lot is known about them, regardless of widespread use. We will all undoubtedly learn more.

I'm not replying directly to you, but the duration of the immunity isn't terribly important past a certain point. The vaccine is much, much safer than infection. It prevents overwhelming of medical resources, and can reduce the community transmission levels to an extent that it can end a pandemic. Those are the primary benefits, not better or worse immune memory. That would just be a fringe benefit if it were the case.