Okay, obviously the happiness part of my argument was a bit of a leap as quantifying happiness is only a recent developed obtained through psychological data. I'd still contend that if early farmers had shorter lifespans due to poor nutrition and a quicker spread of disease and also worked longer hours to grow these meager crops in the first place, it makes some sense to make the leap towards saying that they were less happy. There was also less independence for the average farmer compared to the average hunter-gatherer as early farming communities became stratified.
Of course it could be argued that the Sumerians had more independence due to the existence of granaries ensuring a steady food supply, albeit lower in nutritional quality. Since humans are naturally risk-averse, you might guess that most of us would prefer the relatively more steady guarantee of agricultural food than the riskier business a nomadic hunter-gatherer lifestyle, (and be willing to sacrifice nutrition for that purpose). But yes, "happiness" is a poor criteria because it is hardly knowable.