If Marx had been born where and when I was - USA, 1945 - is there any chance he'd have looked at the condition of the US working man in 1965 and thought about how the capitalists were screwing over the proletariat? I don't think so. He'd have taken one look at the Soviet Union and wondered what kind of crackpot thought a dictatorship of the proletariat made any damn sense at all.
The capital/labor competition is all about bargaining power, which, under our political system, enabled workers to enhance their position rather steadily until around 1970. Then, those worker-voters put on their consumer hats and started importing cheap stuff from abroad. If American workers only bought American. American workers would have better wages. I strongly support prohibitive tariffs on low-wage goods.
I don't take the "access to capital" argument seriously. The idea seems to be that if every person had enough capital to be a capitalist, every person would be a capitalist. Ain't so. Entrepreneurship is a relatively rare talent, as is the ability to allocate capital. Marxists grossly underestimate the scarcity of that talent.
Anyone with a 401(k) plan IS a capitalist to that extent. But most such people need someone to organize their efforts as workers. Capitalism makes the maximum use of the distribution of talents in an economy. The idea that anyone with money can be a capitalist is just wrong. (Hence the saying "Rags to riches to rags" in three generations.)
Electoral politics served the working man well until being white and male became more important than being paid by the hour. Trump has captured the working man's vote, not because he appeals to the working class, but because he appeals to people who happen to be in the working class - people whose whiteness and maleness are the chief source of their self-esteem. These people say they are concerned about economic issues, but if you drill down, and consider why they think Joe Biden, a true supporter of labor, was worse for them than Donald Trump, a proven enemy of labor, the only possible explanation is their race and sex.
As a materialist, Marx would understand that American politics stopped being industrial relations in 1964. Since then it's been about identity. He was far too smart a man to have been a Marxist.