The discussion is being limited by semantics. "Designed", "evolved", "natural", etc. etc. are relevant, but missing a main point.
We are designed to procreate. Nothing more. This is why there are dozens if not hundreds of ailments and degradation associated with old age, because
evolution only cares about getting us to the point of procreation.
We have equipment for digesting meat, true. While being far from optimized from and designed to consume only meat, we certainly CAN get benefits from
eating it.
But this must be thought through carefully. Just because eating a certain kind of food helps you get to the point of being sexually active and thus
continuing the species, that is NOT evidence that such a diet is the healthiest for us in the long-term. It just means that it sustains us long enough
to have sex.
The same applies to our canines, the enzymes we produce, and other food-specific evolutionary traits - just because we have them it does not mean that
they help us or play a role in long-term health.
The ONLY way to determine whether or not a certain food is healthy in the long-term, is to conduct large-scale epidemiological studies. Has this been
done? Yes,
The China
Study is the largest one in existence.
It basically concludes that whole grains & vegetables are strongly associated with a decrease in dozens of health ailments, while animal proteins are
strongly associated with an increase in the same health ailments.
It's disputed, but not by anyone of even remotely comparable authority. There are hundreds of small studies done on health effects that show
contradictory results, but when you take the inherently-more-accurate largescale studies, with data on over 50,000 people, the results are very clear.
So in conclusion, a vegan diet with B12 supplements is the healthiest. That's what the actual SCIENCE says. If you're genuinely searching for the
truth of the matter, then you can't harbor pseudo-logical rationalizations based in a subconscious confirmation bias. (we have canines, therefore we
must be meat eaters!)