You're assuming socialist/communist economies must, for some reason, be run exactly the same as capitalist economies. Of course if you're trying to mix both it will collapse.

The point of Marx isn't that we should create markets where the value is decided by the amount of labor. The point of Marx is that if Labor creates value, then Labor should be in charge. The problem being that Labor is hard, so the end goal cannot be to maximize Labor (or value), contrary to your implied way of thinking were the most value must be created.