In my experience, sigmoid has a smoother gradient in very light areas, e.g. like in this case around areas with sensor clipping. This avoids the typical halos or artefacts of filmicrgb. With the reconstruct tab in filmicrgb you can correct this to a certain degree but this needs a bit of experience and extra care.
See:
Taken from: https://share.streamlit.io/jandren/tone-curve-explorer
Maybe @jandren can answer this with a more theoretical background.