[claudiawerner]

It's worth adding to this: even if the LTV would not hold in its "quantitative" form, which it is often only taken to be, even given the power of financialization in the last century there is reason to believe it would hold at least qualitatively. Several leading Marx value-theorists argue that the theory does not work (or could not work) on the level of the individual commodity, as illustrated by Marx, but only on an aliquot representative of the lot.

Next, theories of exploitation regarding labour are going strong; they don't feel challenged by the idea of the financialization of social labour. For example, there is the theory of unequal exchange (UE) exploitation in which one agent (the exploiter) among other factors contributes less labour than the exploited, but receives the same or greater amount of labour back (i.e in the form of goods and services). There are two principles at work by which analytical Marxists have analyzed exploitation: the Profit-Exploitation Correspondence Principle and the Class-Exploitation Correspondence Principle. I'd recommend looking at the work of Roberto Veneziani and Naoki Yoshihara (both academic economists) on this matter.

Finally, there is some work arguing for the fact of exploitation or the status of the LTV in financial capitalism[0][1][2]. I would not say that financialization poses a serious problem to Marx's value theory, which is primarily a social theory of production - any society must reproduce itself through labour, which forms the material basis of survival of all within that society. There is disagreement as to how the LTV works regarding "non-freely reproducible" commodities, which in today's capitalism come in the form of goods protected by copyright and trademarks. The theory Marx proposed was never meant to deal with this, so I wouldn't say it's a defect in the theory, only that the theory lacks some explanatory power. But neoclassical theories of value also lack the ability to explain the price of such goods.

[0] https://journals.sagepub.com/doi/pdf/10.1177/153650421348770...

[1] https://www.mtholyoke.edu/~fmoseley/Working_Papers_PDF/money...

[2] https://scholar.google.co.uk/scholar?hl=en&as_sdt=0%2C5&q=ma...