the main argument I see for rail is that it doesnt get stuck in car traffic, which should make it easier to keep to a reliable schedule and speed, and that it can have a higher capacity per vehicle. Those would seem to indicate that it should be better than busses for routes that are very busy, provided of course that the rail infrastructure is actually good (able to do a reasonable speed, have reasonable reliability, and separated from other modes of transit to as to not cause conflicts at crossings). If your trains are so slow you can beat them by walking, and directly cross the roads and bike paths, then its not trains as a concept that are the problem, its that you have rather bad trains.