If vitamins were truly 'snake oil', then plants would not be needed, either.
A multi mineral pill is VERY beneficial, as well.
Vitamin C over rated? Why do most animals [not humans] make this in their own bodies?
Rickets and scurvy were once rather common. How did they get addressed and cured? And why is iodine added to table salt?
Of course a good diet is great, but at minimum, extra vitamins/minerals are great insurance. It is TOUGH to eat right - we don't know what is in the food products anymore. and that includes vegetables.