Yes, Carson was one messed up dude. But....
His job was to be entertaining while allowing the guest to be the star. He had to ask questions that would allow the guest to shine. He had to stay up on current events and the doings of the various guests that week. And on top of that, he had to make it look easy, because no one wants to watch a man who's struggling when they're trying to wind down and go to sleep.
The tribute to his talent is that there has never been anyone who filled that position who did it better, or even as well. Some carved out their own niche, but I think all of them would have to admit that Carson was the best, hands down.
And yes, he was a miserable man to work for, and obviously be married to. When he caught his wife Joanne having an affair with ex-NFL star Frank Gifford, he couldn't handle it. But he'd cheated on her every chance he got. He was entitled, apparently.
Some of the biggest talents are the biggest jerks. One comedian said that the bigger the comic, the bigger the jerk. This was back in the days of Jackie Gleason, who, it is said, was a colossal jerk. I assume it's insecurity.