This biggest most is high-quality data. Both their proprietary datasets (WebText, WebText2 etc), but also now their human-annotated data. Another secondary moat is their expertise with training models using PPO (their RL method), they can get results that are quite better than other labs. I say this moat is secondary because it's possible that you can get similar results with other RL algorithms (e.g. DeepMind using MPO) and because maybe you don't really need RL from Human Feedback, and just fine-tuning on instructions is enough
I find OpenAI having exclusive access to that kind of high-quality data more concerning than them having access to their current amount of compute and currently trained model. A couple of million dollars worth of compute is in the realm of any medium sized research university, larger company or any country worth of mention. And seeing as Moore's law still applies to GPU, the cost will only fall.
However high-quality data is scarce. I would be willing to fund a proper effort to create high-quality data.