In case you wanna give it a shot: I gave writing samples of myself from chat and emails to a self hosted LLM, telling it to extract the writing style deviations, key elements, common phrases, symbols, patterns, etc. Then gave that as a "answer it this style" system prompt expansion - works like ... Quite okay. Still need to go over it or course but it doesn't sound like marketing bullshit but conveys what I want.

Completely agree with your general assessment though! They're getting better but the marketing machinery is crazy in their claims.