The math doesn't work, because you are forgetting those that died already that if they had lived, would have been a coronavirus victim. It's survivorship bias.
For example, let's say the mean age was exactly 75 y.o., and that the coronavirus killed 100% of people 75 y.o. or older and 0% less than 75. By your logic, it would have no effect at all.
Another example, again with a 75 y.o. life expectancy, suppose it killed 100% of people 80 y.o. or over and none under. By your logic, being infected by coronavirus would add 5 years to your life expectancy.
For example, let's say the mean age was exactly 75 y.o., and that the coronavirus killed 100% of people 75 y.o. or older and 0% less than 75. By your logic, it would have no effect at all.
Another example, again with a 75 y.o. life expectancy, suppose it killed 100% of people 80 y.o. or over and none under. By your logic, being infected by coronavirus would add 5 years to your life expectancy.