That may well be true. But I'm not convinced that modern economists are doing any better. For example, consider how much economic work is still based on the utterly flawed concept that humans are rational in a classical sense.
It is not. In its descriptive mode, economics captures animal spirits well. In its prescriptive mode, yes, this is assumed. But rationality is a simplifying assumption, with work then done to explain why the reality observed in the descriptive mode diverges from the predicted behaviour of rational actors. Put another way, the rationality assumption is part spherical cow, part “what would we do were we rational?”
Rejecting modern economics for the rationality assumption is rejecting modern physics for its use of frictionless environments.
If you ignore the social aspects of capitalism and economics completely, sure, Marx doesn't look like an Einstein. If you include those, that changes, doesn't it?
EDIT (a long one): Recently I read "Faster, Cheaper, Better - A history of Manufacturing (pretty sure that's the right title, it's in a shelf at home right now) about the history of manufacturing from the stone age to LEAN and beyond, written by a former Toyota LEAN guy and current Professor at Karlsruhe University. Great book, can only recommend it. It is showing well researched examples for each period, including my personal favorite the Venetian Arsenal. And I totally agree with the author that we, as man kind, came out better every time we improved manufacturing. In the long run, in the short run we paid incredible high prices in health, lives and social issues. These short term consequences are just glanced over in this book, hand waved like "yadayadayada, child labor and harsh working conditions bad,... things improved, society better now".
Marx lived during the industrial revolution, he saw those problems first hand. He saw that people with capital got rich, exploiting poor people and driving whole societies and professions into the ground. The Luddites are sold as backwards thinking folks today. Back then, when you just lost your own, small workshop that provided food for your family too a manufacture, when your own, and your kids prospects, changed from stable income to ruined health, 12 hour work days and being treated as cattle, they seem to be quite reasonable so.
That Marx was the only prominent (there were certainly more, Marx being the most famous) economist looking at those issues says more about economists and politicians of the day than it says about Marx.
That those social aspects of our technological improvements are glanced over also tells a lot about us. We are in the middle of a second industrial revolution, one that is aggravated by climate change. We will have a ton of those social issues down the road. And we are not thinking about those enough. That we basically have to fall back to Marx to get some potential answers speaks volumes about modern economics, social sciences and engineering.
Could you expand on that?
He was working with flawed economic concepts, like the labor theory of value. He tried and failed to relate "value" derived from labor to actual market prices. (We now know that the problem he set up was even logically not solvable.) The "economics" you find in Das Kapital is essentially a zeroth-order approximation to what would be considered economic reasoning today, a bit like Aristotle's physics compared to Einstein's GR. It is of some very niche interest for things like input/output analysis, which is important to computable simulations of the economy. But for anything else, it's just not useful.