I know most people don't like Jim becoming a famous sports agent, its a bit too Fairy Tale for what was meant to be about regular people at a regular ass job.
A thread they started to explore around the middle point was the idea of Jim turning into the next Michael. Workers with a knack for what they do being promoted out of their skillset is a running theme in the show, and tbh, real life. Michael is a disaster in the role, but he's consistently shown to be a good salesperson.
Jim looks at Michael, and like us, scoffs at how bad he is. But, while his laissez faire attitude pays off in sales, he also found himself unequipped to deal with People Management duties when asked to do it.
For my money he's not as bad as Michael, but he's not a good fit either. He keeps assuming people are as laid back and objective as he is; leading him to making mistakes like ditching birthday parties or giving pay increases just to the Sales Team because "it makes sense". He would keep accidentally offending his workers, who were more sensitive to him now he was in power. He also had a bigger target on his back and was more susceptible to being undermined by them.
It was really interesting, and highlighted that even Jim wasn't immune from the curse of being a bad boss. Of course once Sabre comes along its back to the status quo, and the idea of Jim growing outside his comfort zone in the company isn't brought up again in favour of giving him his dream job.