Now writing is something totally different. In some cases writing ability is not about writing, it's about your thoughts and understanding of life and human nature.
You could simply become a better writer without not writing anything by just observing.
If you are using an LLM to write, what is the purpose of that? Are you writing news articles or are you writing a story reflecting your observations of human nature with novel insights? In the latter case you couldn't utilize AI in the first place as you'd have to convey what you are trying to say within your own words, as AI would just "average" your prompt or meaning, which takes away from the initial point.
With code it's desired that it's to be expected, with good writing it's supposed to be something that is unexpectedly insightful. It's completely different.
To become a better X to must do more of X. There are few shortcuts worthwhile.
Although we were discussing about the decay of skill in something. While in some things the decay is super clear (as in running - pace, not the technique), I think there's many areas where there's no clear decay and other activities will actually significantly boost it, and any decay that there is, will be removed in just few days of practice or remembering.
There's many more ways to evaluate a writer skill in terms of what they are doing vs what is coding. Coding can be creative, but in most cases you are not evaluating coding as writing, unless it's possibly technical writing, which is still different compared to coding.