Comparing the rates only makes sense if one believes the risk is distributed equally among the two populations. However, the most vulnerable are the most likely

Comparing the rates only makes sense if one believes the risk is distributed equally among the two populations. However, the most vulnerable are the most likely to be vaccinated, and the least vulnerable are the most likely to be unvaccinated, so the vaccine could still be very effective even if the rates of hospitalization are equal, or even worse for the vaccinated population.