Marx's conception of the "working class" is a thing that no longer exists; it was of a mass, industrial, urban working class, held down by an exploitative capitalist class, without the modern benefits of mass education and free/subsidized health care. The inevitability of the victory of the working class was rhetoric from the Communist Manifesto; Marx did anticipate that capitalism would adapt in the face of rising worker demands. Which it did.
Moreover, you would know only if he was wrong about the victory of the working class after the end of capitalism. The bourgeoisie cannot win the class struggle, as they need the working class. So either the central contradiction in capitalism will change (the climate crisis could potentially do this), capitalism would end in some other non-anticipated way (a meteor? some disruptive technology not yet known?) or the working class would win. Until then, the class struggle will simply continue. An eternal capitalism that never ends is an impossible concept.
pt. 1: Whether he was right or wrong was pertinent. You can find plenty of eminent contemporaries of Marx who claimed the opposite. My point was that this is an argument made about technological change throughout history which has become a cliché, and in my opinion it remains a cliche regardless of how eminent (in a narrow field) the person making that claim is. Part of GP was from authority, and I question whether it is even a relevant authority given the scope of the claims.
> Was Marx Wrong?
pt. 2: I was once a Marxist and still consider much Marxist thought and writing to be valuable, but yes: he was wrong about a great many things. He made specific predictions about the _inevitable_ development of global capital that have not played out. Over a century later, the concentration of wealth and power in the hands of the few has not changed, but the quality of life of the average person on the planet has increased immensely - in a world where capitalism is hegemonic.
He was also wrong about the inevitably revolutionary tendencies of the working class. As it turns out, the working class in many countries tend to be either centre right or centre left, like most people, with the proportion varying over time.