On the companion character in detective movies trope

I'm wondering whether this trend in the Benoit Blanc films where the detective allies himself with the outsider/persona non grata among the characters is common in other detective novels and adaptations.

In Knives Out, Blanc bonds with Ana de Armas' nurse character. In Glass Onion, there's the outsider of Janelle Monae's spurned former colleague. In Wake up Dead Man, Blanc has Josh O'Connor's Father Jud, the idealist fighting alone against a fire-and-brimstone parish.

Is this trend of the detective finding an outsider ally on the scene something that was commonly seen with the famous detectives like Poirot, Columbo, Miss Marple or Sam Spade? Just wondering whether this is more of a Rian Johnson trend or something very widely seen across these genius detective stories.