Parable: 100 guys with shovels came over to my yard and dug a swimming pool. This demonstrates the value of labor.
Except it was my neighbor who wanted the pool, and those shovels were built by a capitalist corporation.
This undirected labor was valueless. In fact, it was worse than valueless. I now have to fix a hole, and someone is out the cost of shovels.
The capitalist who purchases the shovels, provides the blueprints, lines, marks, supervisors, and arranges the contract for the pool in the first place has more investment in the project than all the labor combined. Their investment is a few hours time. His investment is more time, more resources, more money, and development.
Therefore, yes, in fact, he is entitled to the majority of the proceeds.
The laborers can demonstrate the value of labor by going to the desert, digging holes with their hands, and waiting for prospective buyers to want to come along and line them with concrete to make pools out of them. Good luck with that.
Alternately, they must develop a source of contracts, materials and capital investment, thus becoming capitalists.
TL;DR: Marx was a @#$ing moron.