High income tax rates vs taxes on capital earnings do that, irrespective of how progressive the income tax rate is, no? I assume the point you are making is that taxing income at a higher rate than returns on capital favors earnings from already-accrued wealth over wealth accural.
As to heritability of earnings, I think there are a number of potential causes:
* Parents pass on knowledge, skills, and values that are valuable.
* Parents pass on actual wealth, or social standing that can help accrue wealth (like helping their kids make business contacts or find internships).
* Parents buy their kids improved education or similar (e.g. childhood nutrition, college test prep, etc).
* Structural biases (racism, classism) tend to reflect attributes that are somewhat or fully inherited (ethnicity, accent, perceived social class).
* Earnings reflect things that are
biologically inherited (intelligence, greed, etc).
I don't find the last point very compelling but I'm including it for completeness. But what I think this list demonstrates is that it's somewhat hard to understand just how pernicious the causes of low intergenerational social mobility may be—the first and last points seem kind of "working as intended" (in a meritocracy); the second and third points are troublesome, and the fourth point is deeply problematic.