If Marxism is a science, then it must be testable and falsifiable. At least, that's my understanding of the scientific process. It's why Freud for example is considered unscientific. This theories have a lot of wiggle room, where any result can be turned into a proof or explained away.
Isn't this what we do with the various leftist projects? I don't know, I'm just confused why it is called a science and not, like, philosophy.
The whole ‘revolution arising in the periphery instead of the core’ thing was a bit of a blow.
To be fair, Marx couldn't have known that laissez-faire capitalism was going to develop specifically into imperialist monopoly capitalism given the information he was operating with. What makes Marxism useful is that despite changing conditions, the methods can be applied to update the theory, which is exactly what Lenin did to update Marxism for the new era of capitalist development.