Completely disagree - a lot of non-native speakers have excellent grasp of grammar, precisely because they have learnt the rules. Native speakers rely on stuff sounding right, rather than necessarily knowing the rules. But following grammatical rules rigidly is exactly what I would expect both from a genAI and a non-native speaker (as well as avoiding figurative speech and idioms).

Try “The Decagon House Murders” by Yukito Ayatsuji - lots of similarities to “And then there were none”