Only a small fraction of all future AI projects have even gotten started. So they aren't only fighting over what's out there now, they're fighting over what will emerge.
This isn't to say it's only going to be an OpenAI market. Enterprise worlds move differently, such as those in G Cloud who will buy a few million $$ of Vertex expecting to "figure out that gemini stuff later". In that sense, Google has a moat with those slices of their customers.
But I believe that when people think OpenAI has no moat because "the models will be a commodity", I think that's (a) some wishful thinking about the models and (b) doesn't consider the sociological factors that matter a lot more than how powerful a model is or where it runs.