If Marx was still alive today, I think that he would answer the question about how modern workers have such better conditions than those in early capitalism the exact same way as when people in his time said that proletarian had better conditions than the peasants before them, which was nominally true.
In any case, the prescriptions of how a 19th century proletarian could improve their life are essentially the same. The idea is that the interests of your employer will always he opposite yours, as a result you will only be able to improve your conditions by organizing with your fellow workers in order to tip the balance of power, and eventually it is in your interests to change the conditions that lead to this conflict to begin with.
To claim that Marx isn't relevant for worker conditions today is to either misunderstand him or misrepresent him. The contradictions arising from social conflict can't be solved by air condition because they are bound to our mode of production.
Marx was inspired by the world around him, which consisted of poor worker conditions [0]. We can say this confidently because recent evolution in the study of ideology tells us exactly this: We are a product of our social and material environment, something we can't escape [1].
Anyway, my point is that the way CamperBob2 discusses the topic of Marx's inspiration makes it sound like a fundamental axiom of Marxism is the poor conditions of the working class and specifically their conditions during working hours. If this was true, we'd be able to conclude that the predictions of Marx [2] would be disproved by the gradual removal of these (poor) worker conditions.
We can show this isn't true by appealing to our shared knowledge about the world, where global inequality is increasing and where worker conflict was at the center of an (almost) successful presidential campaign. We can also show this with empirical data, where our shared knowledge may fail us. For instance, Marx predicted that the global rate of profit would continue to fall, the reasons for which are beyond the scope of HN. This has been demonstrated to be true by many Marxists along the years, of whom the most prominent since the rise of the IT-worker is the economist Andrew Kliman [3].
[0]: See Marx's theory of alienation and the concept of reification, for instances of this.
[1]: In particular, see Anthoni Gramsci through Louis Althusser and Slavoj Zizek.
[2]: Ranging from social conflict theory to capital accumulation, the tendency of the rate of profit to fall, the value-form and social conflict theory.
[3]: “The Persistent Fall in Profitability Underlying the Current Crisis: New Temporalist Evidence” by Andrew Kliman
Marxism isn't a normative ideology. You could be a despotic monopoly leader and still be a Marxist. Whether worker conditions are good or bad at any instant in any place has no bearing on Marxist analysis.