For starters, you ask for real evidence of plants being necessary in the diet of homo sapiens but then provide no evidence of your own to back your claim that humans are obligate carnivores.
Before I continue: I studied evolutionary anthropology and primatology in university, and practiced the Paleo diet for 4 years, and I’m all for eating appropriately raised meat in sustainable quantities. I share this information for two reasons: firstly, I’m fairly educated in the topic of primate and human evolution, and secondly, I have no anti-meat-eating agenda.
Do you truly understand what an obligate carnivore is? An obligate carnivore is an animal that doesn’t possess the ability to break down plant matter into usable nutrients. More specifically, it means lacking “the enzyme needed to split carotene, obtained from plants, into vitamin A.” If we think of this in regard to something as basic as house pets: the domestic cat is an obligate carnivore. Sure, it can eat non-meat items, but it’s not even capable of digesting them, and therefore receives no nutritional benefits, and in more cases than not, plant matter is even toxic to them. Not even dogs are obligate carnivores. In reality, there are very few obligate carnivores in existence — humans are definitely not one of them.
Do you have any idea how difficult it would be for primitive man to live solely off of meat? Modern chimpanzees have a hunting success rate of between 54–82% but they have never been observed killing an animal larger than a small antelope. This would only be enough to feed (possibly) one meal to each member (up to 150) of their community. As such, the chimpanzee diet is only 3% meat. That means only nine days out of the year are meat days.
Humans are a type of great ape. There aren’t any great apes (extinct or otherwise) that we know of that live off of meat alone — nor even mostly off of meat. Even if you were to claim that our digestive tract is more similar to that of a more ancient primate such as a prosimian, you’d find that the only prosimians that live solely off of non-plant material are insectivores. And there is no evidence whatsoever to suggest that humans evolved off of insects.