This is in no way challenges the claim of the many, highly qualified experts who believe there is a problem with concentration of the wealth at the top.
The fact of progressive taxation only shows that the "system" has
some mechanisms to redress the plight of the poor. But to argue that progressive taxation undermines the argument that there is a problem of wealth being concentrated in the top 1% is like saying that the fact that we had a cold winter here in, say, Switzerland, undermines the argument that the earth is getting warmer. The big picture data is clear - wealth is flowing to the top:
From Wikipedia:
In Inequality for All—a 2013 documentary with Robert Reich in which he argued that income inequality is the defining issue for the United States—Reich states that 95% of economic gains went to the top 1% net worth (HNWI) since 2009 when the recovery allegedly started.[8] More recently, in 2017, an Oxfam study found that eight rich people, six of them Americans, own as much combined wealth as "half the human race".
This is the problem with some who adopt your position - hand-waving arguments with no substantive evidential support.