Whether that's through prompt engineering or RAG, or some other technique, the value is in someone else spending the time to think of a UX that helps accomplish a specific job.
If you know what you want and how to do it, then likely fiddling around with prompts can get you pretty close, but people are busy and don't have time to test asking chatGPT 500 different prompts to get one that works well, or hunt around for examples to feed into context or into a RAG index.
There's an asymmetry of information and effort developing the pipeline/context/prompt construction involved. And this is what add's value.
Not simply a chat window and passing whatever the user types in, to openAI's API.
Why do people pay $100 to call out a plumber when they could buy a wrench and the washer they need for $10 total? They are irrationally invoking an expensive wrapper around the "real" business which is plumbing hardware supply!
Possibly you have a very tech centric view of what a startup is?
There's lots of ways you can create value and find PMF that a chat box or API alone can't reach. Marketing / reaching new audiences, design & ux, workflow, integrations, scheduling, oversight / moderation, testing and validation, trust, community building, regulatory compliance, etc etc etc.
We know it is a ChatGPT wrapper. We know how to use ChatGPT generally. But that’s not that broad a group really.