The US ranks very high in terms of absolute mobility. Measures of relative mobility are only comparable between countries if they have similar wage compression curves, which is also partially a function of country size. US wages are much less compressed than in Europe -- see also: engineering wages -- so they aren't meaningfully comparable in relative terms.

Given two countries with the same median wage (PPP), a 20k increase in income in one country may be relatively "economically mobile" and a 40k increase in income in the other is not, even though the income increase is much larger in real terms. When average people talk about economic mobility, they mean the second case; using relative mobility is misleading.