Hybrid()
Death Awaits You
That hypothesis about having to work harder is interesting and makes some sense. But it is also true that dairy is just not as full nutritionally, walaal. Not really any taurine, creatine, carnosine, carnitine and even certain vitamins I can't recall off the top of my head and not much of any iron from what I recall which is probably why our ancestors liked to mix in blood. Eating an animal, especially nose to tail, is a lot more complete and nutrient dense and surely contributes more to why HGs looked more robust. If hard work was the real issue then simply downing more milk should be the pastoralist's solution for being as perfect a specimen as an HG but it doesn't work by the looks of it.

Milk vs Meat: Which Protein Source is Better For You? - BioTrust
When it comes to milk vs meat, which of these high-quality protein sources is best? Coach Tim is on the case and is ready to crown a winner.

In terms of DIAAS score, milk sets the bar at1.32 and beef at 1.10
Red Meat Protein vs. Dairy Protein | Livestrong.com
Protein is an essential part of your diet, but your choice in protein sources makes a difference. Red meat and dairy are similar in their benefits .
Yet another measurement of protein quality is the biological value, which reflects the usability of the protein in a food. When you eat meat or dairy, just a portion of the amino acids are incorporated into your cells for muscle growth, repair and function. Scientists can measure the biological value by calculating the ratio of nitrogen used for tissue formation divided by the nitrogen absorbed from food. Milk has a biological value of 91 versus only 80 in beef. This means that the protein consumed in milk is slightly superior in terms of your body's capacity to use it compared to that found in beef.
Also, out of all the essential amino acids, there’s a key trio that helps you build/maintain muscle: leucine, isoleucine, and valine. Of these 3, leucine is the muscle-building powerhouse and if you look at the chart below milk is slightly superior than beef.
Basically, diary is just as effective as meat for muscle building/maintenance. Vegetarian bodybuilders get most of their protein from dairy and eggs and they've proven already they can build muscles.
Still HG had more muscle mass and stronger bones which their diet was the main contributor. My theory is that HG were able to consume large amount of meat on the days they hunt and had access to organs such as the liver/kidney which are extremely nutritious and although they didn't have access to meat everyday, they were more energy efficient than pastoralists and farmers.