Yes, Fris0uman essentially hit my point. In the long run vitamin deficiency will get you, because unlike meat, the other main source of proteins and fats, most nuts don’t contain iron or vitamin B12. So it’s a slow death from nutrient deficiency any way you slice it since acorns have virtually none of the most important vitamins humans need.
The point that you can get around this problem via multivitamins doesn’t really go against it since they’re a consumable resource you can’t make by yourself. That’s a playstyle consideration and should actually be supported. Nomadic players subsisting on acorns and raiding towns for multivitamins feels like an excellent example of emergent gameplay and the PC is still walking the line of getting scurvy, calcium, and iron deficiency, should their supply of finite multivitamins run out through sheer bad luck.
As for the prep time acorn preparation largely consists of boiling two pots of water and transferring it between them, plus the time to hull and chop them. In game, one handful of acorns takes 24 minutes to prepare and a handful of acorns is listed at .07 pounds, or 1.12 oz. that means it takes nearly a half hour to prepare one ounce of acorns and you’re using a half a liter of water to do it. Making it take more time would quickly push it to even more ridiculous levels.
EDIT: Fris0man, to answer your question, in reality you technically can get all your vitamin needs from multivitamins, but the big three (carbs, protein, and fat) need to come from food. And you generally need at least two in sufficient amount to not suffer serious health issues. Look up “Rabbit Starvation” to understand the effects of having only protein without enough carbs or fats.