By and large, I don’t disagree with your observations.
However, economic issues will not — in the absence of an unforeseen 2019/20 economic meltdown — decide the Presidential election. Trump’s America has been economically prosperous on the whole, even if a lot of that prosperity doesn’t result from his policies. The tax breaks made sure that the election in 2020 will be decided by issues of moral significance (and climate change), and who can win the battle for the hearts and minds of voters in this regard.
This economic upturn applies to most countries (perhaps with the exception of Germany and France, who have fallen victim to the economic flaws of the single currency), and so the disconnect between progressive politicians and voters on race, gender, and LGBT rights will be significant. The article was chiefly designed to explain why the trend is that progressives are pale, male, and stale, rather than to diagnose issues with this. As a personal observation, though, the Democrats would be well-served picking someone like Beto O’Rourke, who holds the centre-ground within the Democratic party, with Biden & co. to his right and AOC/Rashida Tlaib to his left.