You don't need to dig to make the diverter. You can also build upwards. And I don't think you even have to make it of concrete. But from the tiny (Electron) to

You don't need to dig to make the diverter. You can also build upwards. And I don't think you even have to make it of concrete. But from the tiny (Electron) to the super heavy (Saturn, N1, SLS) they all used some form of diverter. It doesn't have to be over engineered like the ones built by NASA. Even the Relativity Terran 1 which only ever launched once had a diverter. Since the Super Heavy and the Starship are lifted into place by the tower instead of being rolled already assembled or rolled and erected from horizontal, it would be far easier for Super Heavy to have an above ground diverter compared to other rocket systems because it is no longer necessary to build the artificial hill and ramp on which to roll it. But the diverter is still needed.