The general consensus among football analysts is that a team's success in the NFL preseason is not a reliable predictor of their regular season performance.
Firstly, it's important to understand the primary purpose of NFL preseason games. They serve as an opportunity for coaches to evaluate their players, particularly newer and less experienced ones, to see how they perform in game-like situations. Therefore, teams often don't play their starters for extended periods in preseason games, meaning the outcomes can be heavily influenced by second, third, or even fourth-string players.
Secondly, coaches tend to use preseason games to try out new strategies, plays or formations, but often they hold back their "real" playbook for the regular season. They are not overly focused on winning these games but rather on preparing for the regular season.
Statistically, there is also little to no correlation between preseason and regular season success. For instance, according to an analysis by FiveThirtyEight, from 2002 to 2017, there was no significant relationship between a team's preseason winning percentage and their regular-season winning percentage.
There have been many instances where teams have had either great or terrible preseason records and have gone on to have completely opposite regular season records. A notable example is the 2008 Detroit Lions, who won all four preseason games but became the first team in NFL history to go 0-16 in the regular season.
In summary, while preseason games can be useful for evaluating talent and testing strategies, they are not reliable predictors of regular-season success.
It's also important to mention that betting on the regular season based on preseason results is not generally recommended, as many other influential factors come into play once the regular season begins, such as player injuries, team chemistry, strength of schedule, and more.