Again, valorization of workers’ labor depends on a process being chosen for labor valorization, and any process chosen to valorize workers’ labor is simply a process chosen.
No choice is objectivity more accurate than all others, respecting actual value of labor.
Equal rate of remuneration, for each unit of time, for every worker, is not choosing a rate different from the value of each worker’s labor, but rather choosing that each worker’s labor has equal value.
Your premise is that some worker’s labor is more valuable than others’, as an inherent or essential attribute of the activity representing the labor.
The premise is false.
Every activity of labor may be objectively described, but such a description encloses the entirety of its objective attributes.
Value is not an objective attribute.
Your objection about the plumber is a red herring.
Activities that are not productive are not relevant to a discussion over how various activities of labor are valorized, because labor is simply productive activity.
Further, the enterprise manages which task occupies each worker at each time. As long as each worker cooperates with such decisions, the worker is being productive within the enterprise, by cooperatively contributing to the social processes of production managed within the enterprise.
Your conception of some workers being more or less removed from a product is simply a subjective feeling, irrelevant to the value of the worker’s labor provided to the social processes of production within the enterprise.