I never buy this. This story is repeated so often in so many places. You hear it about Tesla all the time "Their dataset is so big because they have all those cars out there no one could compete!". But what do we see every time an actual technical article about building something with AI comes up? Throwing a shit tonne of data at a model doesn't work. The number 1 most important thing about training neural nets is carefully grooming the training data so that the NN learns what you're actually trying to teach it, and doesn't just cheat your tests. So no, I don't believe the 5 millionth user typing "Write a monologue in the style of Benoit Blanc about the Johnny Depp/Amber Heard trial" is helping.
I'm not saying there's no incumbency advantage - there clearly is, which is one of the reasons why Office is still dominant. But it's not about raw data, yes you need data, but at the scale that tech giants operate, multiple companies can have that scale of data, and certainly there's atleast a dozen companies that could scrape the entire web if they wanted to. There's also the simple fact that the team that built OpenAI is probably just... better at building AI products, so it's not really surprising that if they pull this off, they will continue to produce the best AI products, regardless of their data advantage.