Developing immunity with natural vitamins and foods is more important for everyone.
only if you are highly malnurished for you to be immuno compromised purely due to malnutrition would nutrition help,
many people are immuno compromised due to other factors.
the body is pretty good at breaking down food into essential nutrients. and the amount of nutrients needed is not much.
when overdosing on vitamins and supplements your body does not store them for later. it excretes the excess via your bladder/bowel. in essence you are just making expensive urine.
those compromised immunity due to other things wont repair their immune system via nutrition. EG diabetics have sticky blood which slows and delays the antibodies because of all the sticky blood in its way not letting antibodies get around the body efficiently.
yes less sugar would reduce the stick blood. but excess supplements wont help. they wil just go to waste
some people have bone disease which means their bone marrow is not producing antibodies.
vitamins and supplements wont fix this as the bones just dont use them in the first place
its like fueling a car. but you dont have the car keys. no amount of fuel will make the car drive if you cant turn on the engine
or
its like having a car with a hole in the fuel tank. just throwing in more fuel will just make more fuel drain out the hole and not really improve the 'gas mileage' ratio. infact you would waste even more fuel per mile.
repairing the hole using proper methods would help.
also adding more fuel into a working fuel tank wont improve the gas mileage either.
again you would need to fix the engine or the tyres or gearbox to improve the gas mileage.
the only time fueling the tank helps is if the only issue is a empty tank due to not fueling it (EG anorexia)
so thinking nutrition is the only fix needed is very narrow minded. and it seem maybe you got your very narrow minded idea from a group that is sponsored by supplement sales companies