This is... shockingly misinformed. To a frankly massive degree.

1. Tribal societies, called "primitive communism," were not at all what Marx was describing post-socialist communism to be. Tribal production was largely based on hunting and gathering, and tiny, communal ownership, rather than collectivized production built on a globally interconnected system.

2. Historical materialism does not pitch history as "linear." It's an advancement on idealist notions of dialectics as humanity advancing, unknown to themselves, a grand "Spirit." Dialectical materialism flipped dialectics on its head, it's matter that drives thought, not a metaphysical ideal that drives movement.

3. Hegel and German idealism have faded because they are idealist, and thus wrong. See point 2. You're confusing Marxism as idealist, and erasing materialism by referring to it as "scientific" dialectics.

4. Marxism-Leninism betrays neither Marx nor Lenin. You just kind of left this hanging without explaining why, so I'd like clarification. Stalin's contributions are largely limited to the political economy of the Soviet Union, such as the policy of Socialism in One Country. Not sure what you mean when you say Stalin lost in the power struggle with Stalin, I assume that's a typo.

5. Marxist-Leninists have no love for the Russian Federation. MLs recognize that due to the RF's lack of the immense financial capital and potential subjects to imperialize that the west already has, despite being a nationalist capitalist nation it's forced to oppose western imperialism, and engage in trade with actual socialist countries like the PRC. Russia has every reason to want to imperialize the global south, but simply lacks the means to do so.

Marx's theories have not failed. Crucially, what I'm picking up on is a surface-level understanding of Marxism coupled with false-conclusions resulting from a lack of depth in understanding. To be frank, I'm a Marxist-Leninist because Marxism-Leninism is successful as a tool to bring about socialism, and a useful tool in identifying the main contradictions in existing society. If you have more specific critiques, we can get into them, but as it stands there's nothing for me to really counter, and I don't want to just stand on a soapbox and tell you to "read more theory," that's almost always unproductive.

It’s a bit of irony, really, that Stalin would name his state ideology “Marxist-Leninism”, esp. as he lost in the power struggle to Stalin.

Assuming you meant that Lenin lost to Stalin, he lost power by suffering several grave ailments—including three strokes—for several years and then dying. He became physically & mentally unequipped to lead.

Marxist-Leninism is a misnomer since it seems to betray both Leninism and Marxism

This is a common belief among Western leftists, including most Western Marxists[1][2].
As some of us say—tongue in cheek—ultras fear the scroll.

I have yet to understand why people are MLs today other than as a kind of pragmatic alignment against Western imperialist powers

That’s not the whole of it by any means, but imperialism vs anti-imperialism has been the primary contradiction of the last 150+ years of capitalism, and likely will continue to be in the coming decades.
V. I. Lenin, 1916: Imperialism, the highest stage of capitalism

I don’t understand the ML love of contemporary Russia

That’s because we don’t “love” contemporary Russia, nor do we think that it’s in any way socialist:
https://lemmy.ml/comment/16985906