The US is very wealth-unequal, especially if you compare it to developed countries:

https://data.oecd.org/inequality/income-inequality.htm

Compared to itself, 30 years ago.

That page doesn't compare wealth but disposable income.

Actually, that isn't shown by your link. Your link's Table 1 shows Wealth Shares by percentiles in 10% intervals. This shows a gap of 39% for the US and 53% for Denmark, between the lowest 90% and the top 10% by wealth. Comparing the top 10% to the bottom 10% shows an 82% difference for Denmark and a 70% delta for the US.

The OP wrote, "the wealth gap in the US seems so much bigger than any other country," which is not supported by your link.

The US is the third worst in that list. If you're content to say "but X is worse", as long as there is at least one X, so be it...

EDIT: And if you want more recent data: https://www.credit-suisse.com/corporate/en/research/research...

America is a lot more like African and South American countries in terms of income inequality than compared to other G20 countries.

It's also one of the few countries with a multitude of multi-billionaires and yet an astoundingly high rate of child poverty.

The question was specifically about developed countries. If you look up the Wikipedia entry on wealth inequality [1] and sort the first column, looking down the list the USA appears to be the highest ranked country for inequality (ratio of earnings between richest and poorest 10%). Notably China is there, and Mexico and South Africa too, among myriad developing African and Central/South American countries.

[1] https://en.wikipedia.org/wiki/List_of_countries_by_income_eq...