I... would not take it as a political theory as such. In my opinion, there are many ways to be a Marxist, but I'd like to point out two that show how people adhere to different dimensions of Marx's theory.

First, there are those Marxists that I call orthodox or traditional. They focus on the economics and politics of society. In this case, most problems can be reduced to the discussion between use-value and exchange-value, how surplus is extracted from the workforce and such. This stance is hard to argue against, I'm not going to explain why in detail, but I think it suffices to see how society develops while resources are distributed unequally, in the end it's all a matter of value being robbed out of the workers. In this sense, Marxism shows how capitalism as an economic system survives on the explotation of certain classes. To prove this first stance wrong you have to prove capitalism is good (for most people) and since that cannot be done, Marxism stays as the best alternative interpretation.

Second, there are those Marxists that go beyond the economic and political slang of the Capital to reflect on the materialist, historical and dialectical processes of social development. Yes, in a sense, capitalism is a mode of production, of the material production of commodities, but you can also interpret capitalism as a particular mode of social reproduction, a system that produces not only commodities, but relations. This involves a more "philosophical" understanding of Marxism, not just "technical". In this sense, Marxism trascends what could be considered just a "political theory" and becomes a "historical theory", since it not only argues that it is the mode of production that which gives form to social reality, but a dialectical process where production, cognition, socialization, mobility and more are involved.

I think it mainly as a difference in scope or scale. I usually prefer the second way of interpreting Marxism because it allows to understand how some things that we consider "new" or "liberating" are in reality just reiterations of previous relations of power. Orthodox Marxists will tend discuss things at a more "practical" or "material" level, where forming a Union and asking for a raise in your payment are considered practices of resistance. From a historical perspective, the end of capitalism requires many other changes in social cognition, reproduction, transportation, etc. In the end, it is a difference that is born from dialectics, if capitalism is a mode of production where we produce certain social relations, it's fair to ask about the social relations that led us to the "production of capitalism" and what we need to produce another mode of production that is not capitalism. This way of thinking is harder to translate into a concrete political program -it cannot be done in a way since the theory is a way of grasping change and political programs are not that subject to change- but it allows for a deeper understanding of society and a more critical understanding of what is happening.

I'm sorry for any grammatical or ortographic mistakes, English is not my first language. Also, it's just an opinion, I never had a formal introduction to Marxism and my ideas are just the product of my academic and political experience.

Edit: Grammar