I did something similar a few months ago, with a similar request never to be "flattering or encouraging", to focus entirely on objectivity and correctness, that the only goal is accuracy, and to respond in an academic manner.

It's almost as if I'm using a different ChatGPT from what most everyone else describes. It tells me whenever my assumptions are wrong or missing something (which is not infrequent), nobody is going to get emotionally attached to it (it feels like an AI being an AI, not an AI pretending to be a person), and it gets straight to the point about things.

Could you share your prompt? Also, does it work well with GPT-5?