It being “scientific” is less about matching the scientific method as we were taught in school. It’s meant to differentiate it from utopian socialism (e.g. everyone will be equal with infinite food and resources) and idealism (e.g. great men changed history because he was a very good speaker). Scientific socialism, or Marxism, is supposed to be grounded in reality, e.g. the world is influenced by many things, but primarily what people need and how those needs are produced and met. That being said, we still observe Marxist critiques, observations, and methods being “replicable” throughout history.
In addition, Sociologists still use Marxist theories and methods in everything but name because they’re simply the best, and even the smarter capitalists use Marxist analysis to help generate profit because Marx’s work was largely about explaining how capitalism works and fails.
And yes, it does matter. We have instances of people who claim to be Marxists and yet fall to unscientific, utopian visions and committed atrocities because of it. For example, Shining Path, Pol Pot, PatSocs/MAGA communism, and various Maoist cults. Some of these were indeed western intelligence plots such as Pol Pot and the GLADIO fascist maoism movement, but the point is that without adhering to the scientific foundations, you are left with gibberish recitations of writers with little substance in practice. Not to mention, you will fall to the liberal recuperation of history and figures.
Another more light hearted example would be The Boondocks. Great show, but even though the main character is a communist and portrayed as the smartest one, the show still paints ‘bad culture’ as the driving force of society.