First I think what he wrote goes beyond them lacking the revolutionary potential and specifically being an active obstacle - I think the words were “significant counterrevolutionary force” and “more likely to sell out to reactionary intrigues”.
But either way, to be honest I don’t see a functional difference between Marx’s beliefs and every implementation of the communist manifesto known to date.
That is, it doesn’t matter what he wrote or believed in his heart of hearts if it can be interpreted in such broad strokes as to allow the implementation of the dear leader mindset with his writings as a touchstone without fail.
And it doesn’t matter what he thought should be done with the lumpen elements if he thought of them as less than, disgusting, parasitical, and even objecting to the cause, (his writings certainly show disgust in my opinion) - true believers to the cause will see them (as they have) as obstacles and will do whatever needs to be done to remove them - as they have.
It’s possible that what you say is true but Marx himself in poverty of philosophy thought you couldn’t arrive without it.
I guess my overall point is that Marx was a man of his time with similar failings and sensibilities of men of his time - amongst other things he was homophobic, he was considering people in groups wholesale in a way that’s rather distasteful, and in a way that allowed later supposed followers to use these writings to fuck over whole populations.
I’m not sure why people are rising up to whitewash these things - they don’t negate the other insights anymore than Newton’s insane occult obsession negates calculus or the theory of gravity.