The nordic countries, which tend to score higher on "Happiness Indexes," are Social Democracies. Social Democracy is a form of revisionist Marxism that believes Capitalism can be wielded for the benefit of all, not just the bourgeoisie.

Unfortunately, these same Nordic countries have been seeing a sliding of the Social Safety Net, similar to what has happened to America following the New Deal (though not nearly as bad yet). Additionally, Imperialism is still the dominant method by which these countries subsidize their safety nets, alongside a dependence on NATO.

US post-WW2 was almost a functioning social democracy, but not market socialism. Market socialism would be something more along the lines of the Labour-dominated era of Israel, or Socialist Yugoslavia.

Yup. The US model is occasionally referred to as "pension fund socialism" (sometimes sarcastically) in the sense that there is a welfare system which resembles a social dividend for the less fortunate, social security which resembles a social dividend for the elderly, and privileged IRA accounts, which resembles collective ownership of capital for the working class. The collective value of US IRA accounts is actually something like 20% of nominal GDP, and social security is like another 10% of GDP. Depending on how you measure it, this makes the actual collective share of the US economy proportionally larger than it was under the USSR or modern day China.

The big thing the US is missing is a healthcare dividend. Also, the welfare layer is arguably much too small, which creates much worse wealth disparity than need be. Still, this is arguably an issue of buttons and knobs rather than the structural issue many make it out to be.