This has nothing to do with mRNA (to the best of my knowledge). mRNA is just a means to an end to get an immunogen into your body. Issues of effectiveness are (as far as I know) entirely due to the immunogen and not the delivery method (ie mRNA).

Vaccines vary in effectiveness. Both the extent of immunity they confer and how long those effects last. A vaccine that's less effective than we might like is still a vaccine. I don't think arguments over what should officially constitute "immunity" are very interesting or insightful - it's a meaningless line in the sand. Ask instead about (relative to the unvaccinated) incidence of death, incidence of permanent effects, severity of symptoms, rate of hospitalization, rate of spread to others, and similar.