I have yet to see any model (close or open source) to get even close to GPT-4. OS models can at best be near GPT-3. Bard is a joke. PaLM and PaLM 2 are not as powerful as Google advertises them to be. Claude is terrible at coding.
OpenAI seems to be doing something special w/ GPT-4, like a secret sauce. It seems like they do have a moat after all. Why do people keep saying it doesn't?
On top of that, OpenAI has been pushing certain standards in the industry, like the <system>, ... (ChatML), funcs, plugins, etc.
Simply having a better product isn't a moat at all. A moat, in reality, is a defensive obstacle that is strategically difficult/impossible to cross.
If competitors can keep improving their products to eventually catch up close to yours, there's no moat because there's no obstacle. To use the castle analogy that "moat" originates from, it's just terrain to cross normally.
A classic example of a moat is network effects, because no matter how superior your product is, you can't get people to switch to yours. That's a strategic obstacle.
Other common moats include things like switching costs (cloud computing lock-in), or economies of scale that are impossible for competitors to achieve (Amazon doing its own deliveries, or Wal-Mart's distribution network).
For more: https://en.wikipedia.org/wiki/Economic_moat