I don't see a major flaw at the moment. I think people like Andrew Yang okay but his ideas are too experimental and his third party could side track the Democratic agenda. That's a reasonable concern, not flawed.
I guess the main flaw on this topic is just that these ideas usually require more federal tax revenue, possibly even double the revenue if they don't want to simply take the money from other social programs. Realistically Democrats can only increase taxes by around 10% before they piss off economists and the upper class, so the main flaw here just comes down to the numbers not being right in 2021.