Okay, I recorded a small series of rolls for attacks that require saving throws. Although the amount of data is not satisfactory, the picture seems to become clear that the "unreliable" Sacred Flame is not as unreliable as it feels.

Link: https://docs.google.com/spreadsheets/d/1YzEY9Tr7LDgg_k3tP8ra6AeazxRH1z969Qx8dIBgvaA/edit?usp=sharing