That's so cool that two people can view a film and come away with such opposing views on what it means. I think that probably means it was a pretty deep movie then or I am very shallow
I think Eddie played Fats to honor his original ambition to the be the best without the hustle. He didn't capitulate to Bert because to do so would have meant that Sarah died for nothing.
But cut off from "big time" pool he reverted to the "hustling" selling counterfeit liquor. Then when he decided to take Vincent on the road and teach him the tricks he tried to get back to the same hustling skills he had known.
But at the end of it he realized that what he told Vince at the restaurant in the beginning is what he really wanted, "pool excellence isn't about excellent pool, it's about becoming something, the best." He realized at the end that he wanted what Bert denied him, the chance to be the best without constraints, without management, without giving anyone a piece of his life.
That's what he meant with "I'm back!"
To me at least.