Isn't 'caldo de res' beef soup? Pot de feu is a boiled beef dinner, in which the meat and vegetables are often served separately from the broth. The Spanish Cocido is closer in concept to Pot, though there is more use of cuts like pork feet and sausages along with the beef.
More or less the same thing, sometimes the Caldo de Res is considered a soup (hearty), sometimes a stew, but the "Pot au Feu" is mostly a stew and, the french version, is not or never considered a soup.
Le Bedaine in Berkeley sells a pot au feu in a broth. Most definitely not a stew. The owner/chef is from France. It was based around beef shank, carrots, celery, onion as were caldo de res that I've had.