I’d be inclined to believe this was happening, due to the fact that OpenAI has had a lot of infrastructure problems, system problems [1], and staff seems underwhelming to handle the general demand. Constantly there are threads here where paying customers complain about having urgent problems and waiting for support.
I do not hold OpenAI in high regards if I’m being honest. There’s an entire moral debate to be had about how they’re making money off of copyrighted material in the first place, etc, etc.
So no one can really say if it is being dumbed down or not. Based on general network stress, or a system where they lower your “brain power” based on a rate limit. I would suggest you do scientific testing to confirm it, but that would cost a lot of money so no one should expect you to.
[1] This was the thread that prompted me to make my first post:
https://community.openai.com/t/api-charged-300-above-spending-hard-limit/104341/3