"Marxism" is a tricky term to use in an discussion because it means such different things to different people. The commonly understood meaning of "Marxism" differs significantly from the socioeconomic theories and models that Marx wrote about.

Even among academics, there are many different schools of Marxist thought.

The evidence against Marx's theories isn't "mass famines, low economic productivity" but his failed predictions of worldwide revolutions.

This may not be fair, but I am going to hazard a guess that you haven't read much of Marx's work and are instead operating off a pop cultural background understanding. That's not a bad thing, that's true of most people. One possible reason for the prevalence of "Marxism" in the social sciences is that I would suspect that they are more likely to have read his work and are probably self identifying as "Marxist" under a pretty different definition of the term than the one used in pop culture.

First, please note that "failed predictions" in my list of arguments against Marxism. My list was, "Evidence against Marxism involves mass famines, low economic productivity, failed predictions, and so on." In other words people who have attempted to apply Marx's theories have created disasters, places which follow his theories do poorly, academics who apply his theories to predicting stuff, get it wrong, and so on. As far as I can tell, any evidence-based assessment of Marxism comes up with a big fat zero.

Second, I wouldn't call myself particularly well-educated on Marxism, but I know somewhat more than the average person. And you're right that a Maoist is different than someone who studies Critical Race Theory, even though both may self-identify as Marxists. (And conversely both may NOT self-identify as Marxists even though Marxist thought has a deep impact on both.) However the "big fat zero" for Marxism includes, as far as I know, all derivative theories as well. But there are enough of them that I know little enough about that I won't recommend being particularly confident of that stronger statement.

Can’t you say the same for capitalism? Much of the support is rhetorical mentioning freedom and rational decision-making while the evidence against capitalism involves mass homelessness, poverty, poor healthcare, imperialism, militarism, bad predictions, and huge imbalances in the distribution of wealth and opportunity.