I associate the hedonic treadmill with a life of advertising-driven consumerism, and the US seems way ahead of Europe in that regard.

In my idea of the hedonic treadmill, one can be on the treadmill but slow it down or even switch it off and cease to run on it. More people in Europe are on the treadmill in the sense that they've maxed out their happiness, but they aren't necessarily running on it. Perhaps of the people who are on the treadmill, more people are actively running on it in the US, driven by the consumerism (essentially addiction) that you point out.

And in some ways you never get all the way onto the treadmill in the US. Even very well paid people can be one layoff or diagnosis away from disaster and there’s a constant undercurrent of anxiety as a result.