Whether Sanders would make a better president than Biden is a matter I'm not sure on, I'm reasonably convinced that he would not have made a better candidate. A more polarizing candidate, yes, and more inspiring to the left wing, but not a better candidate overall. Some of his keystone positions like Medicare for All don't turn out to be very popular even among democrats.

Say what you want about the process, but he did lose the nomination. If you think that's just because the establishment was being unfair, think of how unfair the opposition would have been in the general election.