As a guy who never followed tennis and just started playing 3 months ago, let me share my professional opinion after watching Djokovic vs Medvedev highlights on YouTube:
Djokovic has more efficient footwork, and more powerful forehand driven from his core. Medvedev seemed to be moving his feet a lot, and his arm-dominated swing gave him a less powerful offense. I think that's why the first set was close, and the second two were not (Medvedev having less efficient style and thus losing energy.)
I'm on the Tecnifibre bandwagon and appreciate all-court players so I'm happy to see Med doing well. He did great at capitalizing on opportunities to hit passing shots and win points at the net. I think if he could pick up a little more core power, and hit the ball a little more in front (thus moving closer to BL) it would give him a much more powerful offense against someone like Djokovic.