Gemini very well might be the biggest threat to OpenAI. ChatGPT has first-mover advantage so has a decent moat, but the amount of people willing to pay $20 per month for something worse[1] than they get for free with google.com is going to dwindle. I'd be very worried if I were them.

[1]: That knowledge cutoff and terrible UX of browse the web is brutal compared to the experience of Bard