In 1976, Bert Jones threw for 3104 yards. That was easily the most passing yards in that season. He threw for 24 TDs, 2nd most behind Stablers 27, and only 9 INTs, which was one more then the league leading 8 for best in the league among starters. He had 15. Y/C, 2nd in the league, and 9.3 AYC, 1st in the league.
Now, I know that doesn't sound like much but in those days, that was a huge season. But even though Jones had that monster year, he was really not a great QB. He was just OK. Average QBs do have great seasons but it doesn't mean they are always great. It just means that they sometimes have years that are great. I don't think it's wise to depend on seasons like that without lots of supporting info the suggests it's the norm as opposed to an outlier.