I don't see this as evidence that economists => inequality. Even if we accept the notion that economists are directly responsible for growing inequality, it's worth remembering that there are disagreements within their ranks.
I would argue this is when most economists lost influence in Washington, while a few like Art Laffer gained massive influence. The New Deal era prior to this was largely motivated by the work of noted economist John Maynard Keynes. Although the causality is debated, the New Deal was followed by recovery and economic growth. Economists gained influence in the public sphere because of the effectiveness, real or imagined, or "Keynesian" economic policy. These folks had lost sway in Washington by the early 70s due to the stagflation crisis[1] and the collapse of the "New Deal coalition" after the tumultuous 1968 presidential election.
The late 1970s was dominated by the ideas of economists like Art Laffer, who took an uncontroversial economic idea "tax revenue is maximized at some point between 0% and 100%" and turned it into "the tax revenue maximizing rate must be lower than our current rate" without presenting sufficient evidence for his claim. This was a convenient for some in Washington who already believed this to be true, and thus the "Laffer curve" was born. The following era of deregulation and lower taxes on the wealthy likely played a large role in increasing income inequality.
[1] The causes of stagflation are still debated, but I am convinced this was directly caused by the OPEC oil cartel using it's market power to quickly inflate the price of oil by 400%, creating a massive supply shock that started the stagflation spiral.