they're going to compete on ad unit economics against a company whose entire bread and butter has been selling ads. All while increasing unit costs to provide their service (like all the AI companies seem to be doing by just having more and more planning layers)

If ChatGPT went away tomorrow everyone who wanted to would be fine just moving to one of the other random chatbots from one of the other providers. ChatGPT is the default name that people know, but I don't think that's the same as a moat. A moat would allow OpenAI to go really hard on pricing and ads, and I don't think they have that margin!