That there is mobility doesn't negate the fact that the rich fared better under Bush than anyone else. And in any case, mobility is extremely slow. Most mobility happens over the course of a generation, so the vast majority in each quintile in those graphs were in the same quintiles in the 1990s.
And we also know that tax dollars collected by the federal government went up because of an increase in receipts from social security taxes, not from personal income taxes.
Historical Amount of Revenue by Source
So if anything the Bush tax cuts were even more regressive than suggested, given how the taxes on capital gains (which favor disproportionately the rich) were cut, but not those on social security (which affect mostly wage earners).
Or, to illustrate it even better:
