I sympathize with people who find writing difficult. But, putting myself in GP's shoes, I can't imagine trying to read my father's LLM-generated memoir. How could I possibly understand it as _his_ work? I would be sure that he gave the LLM some amount of information that would render it technically unique, but there's no way I could hear his voice in words that he didn't choose.

If you're writing something for an audience of one, literally nothing matters more than the connection between you and the reader. As someone with a father who's getting on in years, even imagining this scenario is pretty depressing.