The median at any snapshot in time is materially better off, but also much more stressed out than people in other wealthy countries about whether they might end up in a very bad economic situation, due to how there is barely any bottom. Subjectively, middle-income Americans don't feel well off and don't feel secure in even what they have. For example, numbers vary based on the specific survey, but about 60-70% of Americans consistently feel high levels of stress about money. I'm not sure that's a course that would've been taken by a 50th-percentile person trying to optimize their own well-being?
One reason Scandinavian countries tend to come near the top of those "happiest countries in the world" surveys (though I don't like the term "happy" for it) isn't from any particular joyfulness, but because the typical household subjectively has very low levels of economic fear or stress. Some of the survey questions that go into that score include things like, do you feel economically secure, do you worry about losing your housing, etc. A huge percentage of even middle-class Americans spend a lot of their time worrying about that (including my family), while the majority of middle-income people from say Denmark don't consider it a big risk to worry about.