Moving Biden left won't do anything. First, it won't change his governing. Second, he won't move left.
The question should be, what do we prefer:
Slide into fascism with Trump, and a growing but out of power Left? Or step back from the edge of fascism with Biden, but with an emboldened neoliberal class of democrats in power? In the second case, the left will be visibly at odds with the neoliberals centrists. With Trump, the left will be sidelined as it is now.
Moving Biden left won't do anything. First, it won't change his governing. Second, he won't move left.
The question should be, what do we prefer:
Slide into fascism with Trump, and a growing but out of power Left? Or step back from the edge of fascism with Biden, but with an emboldened neoliberal class of democrats in power? In the second case, the left will be visibly at odds with the neoliberals centrists. With Trump, the left will be sidelined as it is now.