Why does Zinn assert that despite party differences among Federalist and Democratic Republicans they were both fundamentally similar?

For
Zinn, the differences between both the Federalist and the Democratic- Republicans were cosmetic.
 Both parties were not actively involved in the enlargement of wealth to more people or
increasing voices of previously silenced groups into the American narrative.  The emergence of
the political parties was something that Zinn perceived to be a condition in which there was
more entrenchment of political, economic,...