See I don't really see it as a heist movie. Sure it has the look and feel of one, but to me it's more of a political satire. Might as well call Argo a heist movie as well, instead of a political thriller, or O'Russells own Three Kings simply a heist movie. As for the heist not being good in American Hustle, well it's based on true events. Even though they stretch the truth of those events a great deal I still don't think they need to make it any bigger than it actually is. I thought they did a good job giving the Abscam story some weight. What sold me on the movie was the Carmine Polito character and his relationship with Irving. While the moral of the story that may be interpreted from that relationship is suspect I think it gives Irvine's character a nice arc and someone to root for. On top of that I don't see the move as Oscar bait. Maybe because the performances are so great and characters rich, sure, but I don't believe the sole intention of the film is to garner awards. And as for the period, it's the late 70's. The movie is centered around the hustle, which was also one of the most popular dances at the time. It has disco dancing, fantastic clothing, crazy hairstyles, a good score and cocaine use. What more do you want from the time period?
edit: oh, and your last note on Scorcese. I get that. Scorcese is certainly the greater filmmaker, but they are very different and O'Russell was clearly mimicking or paying homage to him with Hustle.