I rather lean towards that belief too. However, I would also say that depending on where we evolved we would likely be better at digesting a more meat or more plant based diet. There are islands (more tropical I believe) where people eat almost no meat because there aren't many larger animals around to eat. I suspect they may very well include some bugs in that diet, however, as they would be plentiful. I haven't looked into that as it wasn't pertinent to this topic, though.

That's interesting that it was a B deficiency, because aren't the B vitamins usually the ones lacking or low in plants? I wonder what meats they were eating. I'd need to look into it more, but ruminant meat seems to be indicated as the meat that has the better nutrient content and larger animals would certainly have been harder for a couple of inexperienced men to hunt down. Rabbits are notorious for being deficient in a lot of the micronutrients we need, so that could go for other small animals as well. It would be interesting to delve into that more. In a harsh climate like the desert the native people would likely have been far better adapted and likely much more knowledgeable in the foods they would need to access to get the range of nutrition they needed. Which reminds me, the Masai men often get mentioned as mainly meat eaters. They also drink a lot of milk as they farm cattle. Again that's ruminants and I suspect that they would also eat some plant foods, because the women do.

It's probably also worth noting that while there are some people who've been strict carnivore for many years, most of them do add in some limited plant foods once they have recovered from their issues, or if their issues are minor they will occasionally eat other foods on special occasions at social events. Most approach it as an elimination diet then once they are feeling better they try other foods out and see what they can tolerate and what sets their issues off.