There is so much opinion and politics polluting any science here, plus pure marketing. (Remember butter is bad, margarine is healthy, no wait, margarine is bad, butter is healthy.)
No ancestors were nearly all vegetarian. Likewise none were all meat and no grain either, Paleo is just a name someone picked to sell their diet.
Having evolved from a common ancestor does not make modern primates a good guess at what our ancestors ate. If it was they likely would've evolved with us.
As someone with digestion issues that has recently redecided to not take in nutrition, meat is concentrated nutrition. Sugar is concentrated calories, the inflammation it causes must not be very powerful as many with this survive off sugar and we already inflame ourselves. There are no studies telling us to not do that. There are studies showing restrictive diets are not good.