Of course, people and eras are rarely portrayed in a way that is 100% accurate. This is true of the Roaring 20s. However, much of these portrayals truly does capture the reality of the 1920s.
It is beyond dispute that the values and behavior of many (but not all) women was changing during the '20s. Flappers were real and they truly were different than women had been previously. However, it is by no means true that all women were flappers or that all young women acted in these new ways. Our vision of the '20s focuses on what was new, not what was similar to the old days. So it is probably fair to say that our views of the '20s overstate the amount of change in women's lives but we must also realize that real changes were happening.
The same goes for gangsters and speakesies. This was the era of Prohibition and gangsters truly did get rich off illegal alcohol. There were speakeasies with jazz music playing. However, the average person (especially outside the cities) was never going to end up in a speakeasy.
Overall then, the image we have of the '20s is somewhat (but by no means completely) exaggerated. Our images of any decade tend to be somewhat caricatured because it is impossible to capture the full diversity of life in any given time period.