Do you think the Inuit, or hunter-gatherers in northern Europe or Asia were getting 50% of their calories from non-animal sources? You know the answer is absolutely not.
I don't want to get into an annoying, repetitive ideological flame war here. What I can tell you is that depending on the climate and the length of the winters, as well as the soil, tribes had vastly different diet compositions. There are numerous studies on this.
Even outside the polar regions to places where fruits and vegetables where not available or were very limited people came relatively recently. For example, in Mongolia it happened about 20 thousands years ago. Moreover, human population there in any substantial numbers appeared less than 10K years after domestication of animals and access to their milk. In Mongolia people living in traditional ways drink a lot of fermented horse and camel milk getting enough calories from carbohydrates to avoid a permanent keto state.
So a permanent keto state from evolutionary perspective was never sustainable.