"A smaller relative slice of a much, much larger pie can still be a much larger piece of pie in absolute terms. The poor are not getting poorer, the rich are just getting richer faster."I don't see where the article claims otherwise.
That said, the point is pedantic: if the share of income in a group gets smaller over time, their purchasing power goes down correspondingly as well. The overall size of the pie matters only to economists.
"Also, the choice of timeline is very suspicious. Pegging the start of the graphs at the end of the Great Depression / WWII skews the graph, as does omitting the context of the 19th and early 20th centuries. This is more about chart-junk supporting a pre-conceived narrative than anything else."
And not including the civil war skews the graph as well. Or the depression of 1893. You can always find an argument like that to justify not believing something that you choose not to believe. Calling it "chart junk" is just exaggeration.