>Similarly, for the modern day US, "is it just to reward people proportionally to hard work, intelligence and the ability to produce things that people want?"

You've reversed the causality. Remember, we're asking for a definition of merit that is not isomorphic to "whatever the current economy rewards". We're trying to ask if we can hold the current economy to an external, human standard of performance, rather than just taking it at its own word that "when the numbers go up, it's good" (with the associated problem that even by this standard, "the numbers" have been growing more slowly and crashing more frequently since the rise of inequality began again in the '70s and '80s).