What if "obstacle B" is a cardboard cutout of Mickey Mouse and "obstacle A" is a person? Maybe you actually could make a better decision sometimes.
Actually, the idea that computers always will make a better decision than a person is hilariously optimistic. Sure, they will make a faster decision, which most of the time will avoid both obstacles, but that's not always the same as better.
There's no doubt in my mind that self-driving cars will improve traffic immeasurably, because of quicker reaction times, but computer-based systems frequently do really stupid things that no human would do. Putting one in a car doesn't make them flawless.