filmic crushes the shadows a bit, while sigmoid shows a bit more details. This leads to a clearer look in this part of the image in the filmic edit.
That is because I set black-relative exposure in Filmic to only -2.09 (calculated by color picker) which is probably a little bit to high, although I’m still able to distinguish the shades of black at my Eizo CS2731. A value in the range [-3.00 … -2.50] gives a bit more headroom in the dark blacks, but with a value below -3.00 the output picture starts lacking global contrast. At the end, its just about personal preferences.
Filmic black -2.09 (left) vs. -3.00 (right)
Watching the rendering of the lamps, I think sigmoid does a better job avoiding halos.
Those lamps have clipped highlights and I’m using Filmics reconstruction, but it doesn’t help here. Therefore Filmic produces a reconstructed area around a sharp circle of blown highlights, based on the settings. Unfortunately I’m not able to find a suitable setting here. Sigmoid, which hasn’t reconstruction, just clips and may look a bit better here. In both cases I find the magenta CA at the lamps on the left machine more anoying than the blown highlights.
To get even closer to filmics result you could tweak sigmoid a bit more, especially the colour processing parameters.
Yes, you’re right. In vector scope (Jz) you clearly see a color shift from blue towards red when changing the color processing in Sigmoid from crosstalk to rgb ratio + rgb power norm, which finally compensates the blue color cast.