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...