I find the debate preparation by each candidate indicative of their character and general approach to everything. Whether you like Biden or Trump, the differences couldn't be more stark. I think of the preparation for the debate as preparation for a test. On one hand you've got a guy who sits down (while holding a full time job) and prepares for eventualities, possibilities, brushes up on details, and goes over issues that may arise. Oh the other hand, you have someone who says "everything in my life has prepared me for this debate" and brushes off the importance of details.
Preparation by anyone is important. Biden clearly understands this and takes a disciplined approach to things. This is in complete contrast to Trump's complete and utter lack of discipline. IMO, this stems from his narcissism and god complex. He's so convinced he's above all of this that he doesn't need to take the time to prepare.
Now, could Trump come off better in the debate? Sure, but all things being equal, preparation and discipline win out.