Oof what a silly naming decision. Deepfake already has an established coherent meaning - it's specifically about impersonation with video/audio/images. Just writing in collaboration with a tool is not deep or fake necessarily.
The closest analogue for text I can think of is when you use an LLM to write in the style of someone else, like Shakespeare. But "deepfake" is a stretch because AI-generated text in someone's style is not particularly convincing that it actually came from them, and wasn't too hard to do manually before. Plus doesn't raise the same ethical questions.
See Lora vs LoRA and many others.