> There is no incentive for their bosses to walk an extra mile to keep them happ, especially when pressing them a bit more yields an extra bit of performance, so they mostly aren't happy about their jobs

That's the theory - but I don't see the distinction you listed ever proven. People do it because it's the easiest thing, that doesn't make it the best thing. I can just as easily theorycraft that happy employees improve production ACROSS THE BOARD, with lasting and compounding results. The studies that argue this never make the distinction you've listed.