Some people here are confusing criticism with evaluation.
Criticism is trying to understand a work as it is. Trying to understand why the photographer made the choices he made, what these choices may have meant to him. Trying to understand what the work might have meant to viewers at the time it was made, trying to understand how that meaning may have changed with time.
Criticism has nothing to do with evaluating—often arbitrarly, and according to one's own criterea—whether a photo is good, bad, whether it could be better if, or worse if.
Stating that adding the lower steps would make a better, or worse, composition is totally irrelevent to the photo that is. Only important question is wondering why Cartier-Bresson didn't put them in. This has nothing to do with hero worshipping. Looking at what is is the only way to begin to try to get into the photographer's mind. That's the mind I'm interested in understanding. Not that of the person who thinks the photo would be a better composition with the lower steps.
Mona Lisa might be a better, or worse, painting, if she were naked. Who knows. Honestly, who cares.