Their data may not be that much better; however Deepmind is still one of the best institutions that study AI fundamentals. OpenAI works hard and focused towards products, but the academic research is far better from Deepmind. So since Google hasn't been trying to put any AI into products really at all for the past 10 years, they're going to have to push a little bit to make the public facing interfaces and put polish on things, but the underlying models they have made are far better than OpenAI (just not the ones made publicly accessible to anyone).