This is a good link and the Practical Engineering guy doesn’t appear to reference a “myth.” Which is a good thing, because there’s nothing mythological about the high performance of Roman concrete.
The answer is no. What is true is that some Roman concrete structures (but far from all of them) are extremely durable because they were optimized for a different set of requirements than modern buildings usually have, notably "needs to last forever as a symbol of the emperor's power". From the 19th century on that has very rarely been a design constraint, so we optimize for other things instead.