"Open up the shadows, and the highlights get compressed."
For me, THIS is what is wrong with curves. Whilst I understand the role it plays, I've never understood why I can't make everything to the left or right of a point on the curve fixed in place and just move another part of it. There's no reason why the entire image needs to be represented by just one curve and to an extent, I get the feeling that the sliders attempt to deliver that.
I wonder if it makes sense to be able to adjust the range of tones over which those sliders operate on?