If you could establish an impregnable firewall between young healthy people and vulnerable people, and you ignore the rare deaths of healthy young people and side-effects of infection, the infection rate among young healthy people would be less important.
But establishing an impregnable firewall is impossible, and long as the boundary between groups is porous, a higher infection rate among the young and healthy will increase the infection rate among the vulnerable, and hence the death rate.
But establishing an impregnable firewall is impossible, and long as the boundary between groups is porous, a higher infection rate among the young and healthy will increase the infection rate among the vulnerable, and hence the death rate.