What is waved by gravitational waves if no medium? Where is the source of energy for gravitational force if no medium? Why light have Doppler effect if no medium? How photons are formed if no medium? And so on.
Any attempt to discuss these topics drops shadow at Einstein, an then he fight back.
I'm not trying to discredit Einstein, or Newton, etc, but we have much more information about Universe than 100 years ago, so we can make better theories. Moreover, "shutup and calculate" is not an answer for physicist, we need explanations.