How do you think America got out of the Great Depression? It was FDR turning the country’s economy from “free market” capitalism into a centrally planned economy during WWII, with much opposition

Wasn't that a compromise, though? He didn't end capitalism (as the left of the time wanted to do) -- he created enough safety nets and job programs to keep it going long enough to recover. And even within the New Deal there were compromises. Part of the reason the New Deal didn't do a whole lot for black people is because to pass it FDR needed the votes of Southern Dixiecrats.

In an era threatened by a climate emergency, anything less radical will not be able to solve or mitigate the devastating effects of climate change.

I absolutely agree that radical solutions are the only thing that can reverse the effects of climate change at this point. But mitigation? Yes, smaller changes can at least help, and they can help quite a bit. Say we do nothing to actually reduce carbon emissions, but we instead open the southern border, offer a fast-track citizenship process, and stop orchestrating coups (at least in the Western Hemisphere). On the scale of potential changes those aren't radical. Hell, Reagan offered amnesty to immigrants in the 1980s. But they'd mitigate the effects climate change will have on an enormous amount of people. If we're talking about material improvements -- and we should be -- isn't the ability to move to a wealthier country and not be treated as a second-class citizen a material improvement? Isn't the ability to build a leftist government in your home country and not have it hamstrung by capitalist opposition a material improvement?

it will prevent radicalization of the US politics and perpetuate the theatrics of “progressives in the house” while people are being denied healthcare

If we wound the clock back to January and replaced every Democratic politician with an AOC clone, Medicare for All would be at the top of the agenda today, just as it was at the top of Bernie's agenda. There would also be a significant climate change plan (the GND) high on the agenda. You might be right that it would prevent radicalization, but you're wrong that it would just be a dog-and-pony show while nothing material changes, because the whole premise here is that we'd be electing people who are genuinely pushing for big solutions to big problems.

We already learned that from Obama, who campaigned as a progressive who will take on Wall Street and give hope to America, and we all know how that turned out.

I don't buy that the existence of one fake progressive means all progressives are similarly fake. Shit, we had progressives prior to Obama who did a better job of walking the walk, so we know that Obama isn't the only option.

Bernie Sanders conceded without getting even a single concession from Biden.

What leverage did he have? What were his other options? Would Biden in any way be obligated to follow through on any concessions?

What makes you think that AOC or other progressives will have the swaying power to resist them?

Again, we're talking about a situation where the establishment is full of politicians like AOC. There's no one to resist.