Biden's record speaks for itself
LBJ was a one term president (1.5 actually, but he ran once), but he is remembered more for Medicare and civil rights than for not seeking reelection. Joe will be remembered for passing more meaningful legislation than any other president in a lifetime.
I think when it's his turn to speak at the Dem Convention, probably the keynote on the second to last night, the cheers and applause will be deafening, and the waterworks will running throughout the crowd of delegates.