I don't see us just eating meat as our ancestors would have acquired knowledge of edible plants and it's a lot easier to gather up plants than trying to hunt or fish if you have edible plants.
The problems we see today is all the refined foods stripped of nutrients.
Nowhere in nature will you find combinations of fat and sugar in the proportions that you find them in our current junk food menu.
Grasses, tubers, fruits, nuts, seeds, small game and eventually big game when weapons came on the scene. That was our ancestors diets.
It was a fast until you found food situation. The biggest problem we face today in the west is obesity. We are huge as a population and it's a disaster for the healthcare system and the people that have to suffer the pain and misery of all that blubber weighing them down.
My diet when I'm trying to be healthy is lots of green smoothies made with collards, spinach, kale, bananas. I feel fantastic eating as much raw foods as possible. My garden produced tons of broccoli this year that I cut up and froze and the flavor packs a punch unlike that crap in the stores.
Meat of course for me it's usually fish or steam cooked poultry. I rarely eat steak or hamburger anymore because I feel like shit after I eat it. Boiled eggs are good. What I'm trying to do is cook my meat without dry heat or oil, from what I've read with the NIH studies it was shown that carcinogens come from how you cook the meat, not the meat itself. Cooking on the grill is not a good way if you care about your health.
As for meat only diet. I see that as a another fad just like the vegan diet. A well balanced diet with lots of dark leafy greens, legumes, beans, nuts, seeds, and moderate intakes of animal protein and that doesn't have to be everyday. Keeping the grains and cooking oils except perhaps olive oil out of my diet.
And of course water fasting for 24hrs every once awhile would be good for anyone's health, I've found that it actually gives me more energy and my almost 50 year old joints feel a lot better.