Yes, Jim Gordon is the actual protagonist of this Batman story, even Frank Miller admits so in notes for the special edition of the graphic novel, but the production crew of the film seem to have forgotten it along the way. Gordon has the arc, the main struggles and even the best fight scene (see below). Cutting down on the Gordon story really doesn't make much sense, even to make room for more Batman and Catwoman, who, again, don't really have major character arcs in this story. Speaking of Catwoman, I would have hoped that one change that would have been made would be her underage prostitute friend; but no, apparently that was an important element of the original vision to keep. Yes, Gotham is painted as a city of the worst sins, but maybe just shift her age up a little to mitigate the creep factor? I think the drugs, corruption, pimps and prostitutes over the age of consent convey the message just fine.
The lack of quality in Batman Year One is a real shame, the Warner Premiere Under the Red Hood and All Star Superman are amazing adaptations, keeping the charm of the source material and making the narrative work in a different visual medium. Given the patchy nature of film adaptations of DC works, I increasingly find myself puzzling over the ones that "work" and the ones that don't. Quality of and adherence to original source material are seemingly not factors, there is no continuity of character, writing and theme. What works for DC adaptations is a nebulous thing that no one, least of all Warner Brothers, seems to be able to get a handle on.