This was actually a good match from Rune. He showed his mental resilience and the tools needed to be a great player in the future.
Two major things he needs to really work on this offseason: Match fitness AND tennis strategy.
I think his match fitness will improve as he gets more experienced and older.
As for his tennis strategy, he needs to be more aware on what type of shots he needs to hit in order to maximize his chances to win the match. For often than not, he goes by his instincts and talent thus you will see a great shot one point, but a bad shot the very next point. I would argue that once he is able to develop his tennis strategies, it would help his tennis fitness level because he won’t have to spend too much energy on different shots.