Our minds and bodies were not designed. They evolved — slowly — under conditions of relatively harshness and scarcity that to a large extent no longer exist. The human "habitat" has changed radically in the past several hundred years. One might argue that we're no longer adapted to our environment. Evolution doesn't work quickly enough for that.
I'd also suggest there was widespread physical and mental suffering in the distant past. It wasn't the Garden of Eden in prehistory.
I would agree that we are no longer adapted to our environment, and this seems to be the cause of many "modern" forms of suffering that are unrelated to scarcity, like mental illness and diseases of over-consumption. To me this implies that we have done a bad job in creating an environment for ourselves. We replaced suffering caused by scarcity (something we historically had little control over) with suffering caused by deliberate choices.
The point isn't that aligning our choices with biological and psychological needs will end all suffering. It's that not doing so pretty much guarantees a lot of unnecessary suffering.
To say that evolution is a "red herring" is absurd. It has literally determined every aspect of our being. You can't move forward without understanding what got you where you are.
So has physics. Why stop at hunter-gatherers, why not go back to the Big Bang? Would you argue that we need to study astrophysics to deal with obesity?
It's not absurd at all to suggest that evolution is a red herring, any more than it's absurd to suggest that astrophysics is a red herring. Prehistoric archaeology is highly speculative at best. I'm not saying it's unscientific, I'm just saying there are a lot of things about prehistoric societies that we could be very wrong about, due to lack of direct observation and evidence, and thus it would a poor guide for our current and future societies even if we decided to base our behavior on our ancestors (which we shouldn't).
No one is saying that we should live exactly like our ancestors.
They did not had diseases of over-consumption, but they had diseases from under-consumption.