Marx has some concept of "socially necessary" labor, but it doesn't really make sense because it wants to treat skill as some kind of simple multiplier as if we can assume that a modern doctor's labor is some simple multiple of a random medieval peasant's labor in diagnosing an illness, which is just a silly and oversimplified model.

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.

What you're getting at vis-a-vis highly skilled labor is known in Marxist economics as the labor reduction problem, and it's complicated (enough so that I wouldn't do it justice trying to elaborate the approaches in the time I have to respond). Marx died with it unsolved and it's a matter of discussion to this day. But you're conflating that problem with the concept of socially necessary labor, which is different and actually addresses the problem you posed (in Capital Vol 1, in the difficult early chapters). In order to produce value, the labor must be socially necessary, and the labor of any number of unskilled workers towards a highly complex problem (eg, treating a rare cancer) would not be socially necessary. It doesn't even have to be that complex. I don't have the skills necessary to make a wedding cake, and any attempt I make to do so would be so inept that it wouldn't be socially necessary labor.

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.

I mean, economics is a mathematical profession. It's hard for me to take his storytelling about things like the freedom of hunter-gatherers and such seriously when I know he wasn't rigorous in the things that are easier to check. Never mind the, err, implementation problems in basically every attempted revolution until somewhere around the point where the Nordic states found a way to subsidize it with resource extraction and found a voluntary version.

It strikes me as incurious to dismiss an entire field of thought because there were errors in a mathematical manuscript, especially when you clearly don't understand the fundamental concepts (I don't mean this as a dig. You just haven't learned them.). Marxism isn't the writings of a long dead guy in England in 1860. It's a living, breathing school of thought that's evolved significantly since then. What you're doing is akin to finding an error in Smith or Ricardo's [edit: unpublished manuscripts, not completed work] work (of which there were many) and using those errors to dismiss all of orthodox economics.

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.