It is unfortunate vitamin C recommendations are all over the map, but we know equivalent animals in weight make roughly 3 grams a day and up to 200+ grams when sick.
You have to be careful in looking at what other mammals make in terms of body weight and applying that to humans.
As we all know, somewhere along the way, humans lost the ability to make vitamin C endogenously. Why? Evolution doesn't normally "forget" capabilities that predecessor organisms previously had, particularly when they are crucial to the organism's viability.
There's a reason humans no longer have the genes to make vitamin C - because humans use glutathione as our primary antioxidant, not vitamin C as other mammals do.
We still need some vitamin C, but in humans glutathone does the heavy lifting so we need less, in fact amounts that can be routinely obtained in a typical pre-modern diet. Maybe you can achieve some benefit by ingesting superphysiological levels, but you're really using it more as a pharmaceutical rather than a supplement (which I have no issue with whatsoever). But saying that humans "should" get as much as 3 grams a day is in my opinion a stretch, since in pre-modern times (back when we were hunter gatherers) I think you'd be pretty hard pressed to find many human populations routinely getting 3 grams a day in their diet. It's not impossible if you are fortunate enough to live in an area where certain superfoods are available (kakadu plums for instance). But there were plenty of populations living in areas with relative poor sources of vitamin C.
If vitamin C was that readily available "in the wild" through diet, most likely other mammals would also have abandoned the capability of making it themselves. After all, every unused capability carries some burden with potentially no benefit, something that evolution isn't prone to produce.
We certainly need some vitamin C, very likely more than the US RDA, but 3 g a day? I have trouble believing that humans were supposed to get that much in their diet.
For some people might there be a benefit from those levels? Sure.