The animation of this film is some of Don Bluth's best work. The story, on the other hand, is heavily influenced by Steven Spielberg, who took bits and pieces of his own family's story as they came to America. Now, my guess is they were not involved in the Wild West (as in the sequel), but for the first time around the parallels are there.
Did immigrants see America as a land without cats and streets paved with golden cheese? It seems absurd that anyone would have this expectation, but at the same time it is not completely wrong. Exaggerated, yes, but compared to the hardships and often death waiting behind in Eastern Europe, the slums of New York might have been seen as a salvation -- in many ways they were!