This is a very simplistic view. The complexity of weather prediction is a factor of both how far into the future and how fine-grained the prediction is. Predicting 1 minute ahead is trivial. Predicting temperature with a 20-degree accuracy a week ahead is trivial. What Deepmind does here is predicting precipitation ~1 hour ahead with a ~1km resolution, and they do it significantly better than existing models. Perhaps not a breakthrough, but a substantial technical development it is.
