Marx discusses how skill (and factors like machinery, etc) factors into value in Capital vol 1. The idea isn't that any labor on any endeavor creates value at a constant rate across all individuals and all time.
Honestly it reminds me of like Marx's non-rigorous "eh whatever" approach to dividing by zero in his mathematical work. While one can define division by zero in non-standard analysis, that involves some actual rigor in how your treat it according to your definitions, not just shrugging your shoulders and doing it.
Can't speak to the division by zero, but it doesn't come up in any of Marx important work. His mathematical manuscripts don't have any significant relationship to his work on political economy.
The revolutionary approaches have not succeeded thus far, granted. There is a branch of Marxism about revolution, but what we're talking about here is a description of capitalism. Marxist revolutionary activities have nothing to do with how potent that analysis is.