Well, yes, because you've just included a significant part of the solution (economic homogeneity) as one of the criteria. When you look back at Norwegian history over the last century, a lot of the shift happened in line with the rise of the labour movement and the rise of the welfare system, and a lot of the beneficial outcomes were visible before the oil revenue even started.

Norway as a result got one of the flattest income distributions in the world, and has relatively high degrees of social mobility, and a culture where the labour movement combined with religious groups (in what some might call a rather unholy alliance) promoted the ideal of modesty. E.g. in Norway sending your schools to private schools long held a significant stigma.

At the same time the US started moving in the exact opposite direction: Executive salaries as a multiple of workers salaries started skyrocketing etc..