I'd emphasize not only that there have been advances in theory but also in, more importantly, the empirical evidence. Marxism is a scientific theory in the sense that it can be falsified, and if you look at the rate of profit over time in most countries and periods, the evidence very strongly falsifies Marxism. Even if someone refuted Okishio, Marxism makes predictions about capitalist economics that simply aren't consistent with the world we see.