I found that, too. One trick with sigmoid, though, is to enable local contrast, and increase the highlight detail there. You can even create a masked instance, and use the multiply merging mode.
Here’s an example (the original, intentionally bland version on the left is not representative of what sigmoid can do, it’s only for illustration purposes; the image is from a PlayRaw):
Only the histograms, before/after:
Filmic allows you to explicitly set the white and black points; sigmoid does not: the latter relies on skew and contrast, but those are not as flexible as filmic’s direct controls.