I agree marx was trying to deal with a genuine theoretical problem
in his theory of production prices, but the question is whether
the theory within which it is posed is right.
If one has a theory that says competition leads to capitals
in different branches earning the same rate of return, then one
has a theoretical problem. But what if this theory is wrong.
What if competition does not work that way. What if capitals in
fact earn profits proportional to the number of workers they
employ?