The public GPT-4 is a fine-tuned model that exhibits mode collapse and has a certain writing style induced by the fine-tuning [1]. This "overly helpful assistant" style can't be fully eliminated with custom system prompts. The GPT-4 base model, were it available, could likely be prompted to act much more like a normal human.

1. This can be seen by comparing the fiction writing ability of the GPT-3.5 base model with the fine-tuned ChatGPT-3.5 model: https://nostalgebraist.tumblr.com/post/706441900479152128/no...