Of course it contains GR as a low-energy limit. Where it can be physically checked, it is equivalent to the existing successful theory; where it makes new predictions, it can't be checked and so is almost certainly wrong. To make progress in physics you need to apply yourself to a real open problem (like "Dark Matter") or get new data (from quantum computers or primordial gravitational waves, maybe). The only good thing that can be said about Wolfram is that he is not paid with my taxes, because plenty of cranks in physics are.