Maybe he is but …
What could possibly be wrong with Einstein’s beautiful masterpiece? From the theory perspective, there are two possibilities. One of them is that general relativity seems to be incompatible with quantum mechanics. The many successes of quantum mechanics in the second half of the 20th century have been dazzling. We have learned how to create quantum electrodynamics (the quantum version of Maxwell’s theory of electromagnetism) and quantum chromodynamics (the quantum version of the fundamental weak and strong nuclear forces). However, the methods that worked so well there fail badly when applied to general relativity, suggesting perhaps that a completely different description of gravity is needed at the quantum scale.
Another possible issue with Einstein’s theory relates to “singularities.” In general relativity, there can exist regions of space and time where the curvature of the spacetime continuum becomes infinite. In fact, Roger Penrose, one of the recipients of the 2021 Nobel Prize in Physics, was instrumental in proving that not only can these bizarre regions exist, but in fact, they must exist! Einstein’s theory, however, seems to have a built-in “censorship” mechanism so that observers like us are not exposed to the gory and dangerous features of these singularities. Indeed, the spacetime singularities in all reasonable solutions to general relativity are hidden behind event horizons, boundaries that forever trap all observers and light signals, as well as any garbage emitted by a singularity. But just because they are hidden behind a veil does not mean that singularities are not a problem.
From the observational perspective, there are also arguments from the world of astronomy suggesting that perhaps Einstein’s theory is not the final word…Clifford Martin Will and Nicolas Yunes, “Is Einstein still right?” at IAI.TV (August 25, 2021)
It’s been a while though. What would replace Einstein’s theories? The war on math?
You may also wish to read: Sabine Hossenfelder despairs over vacuum energy. Rob Sheldon responds. These specialty controversies are an interesting backdrop to the current war on math. Sabine Hossenfelder and Rob Sheldon would likely agree that 2 + 2 = 4. But survey the vast degreed hordes for whom such a statement is an instance of white supremacy and colonialism and we will see the real problem facing our civilization: Far too many people have degrees (and grievances!) but no insight into what knowledge is.