I agree, however stuff like Novaskin and Piskel which both have line tools, don't have gradient ones, and Novaskin's line tool is very low quality. Both of those editors are very popular for not just skin making, but pixel art in general (especially Piskel), however none of them had a gradient tool, which meant they had to do it manually, or export their current sprite and edit it in another editor. (I won't talk about Asprite here, as I don't have a license for it, and haven't seen much of it.)
As well, on stuff like the mobile version of PMCSkin3D, it's pretty tedious to get lines/gradients right, as mobile screens are small. And it takes lots of time. Incorporating the line tool would solve all these issues and more, and so would a curve/distortion tool, for circles and the like.
Line tool for PMCSkin3D
If this is going to be accepted, can we also have a gradient line tool? Gradients take too long to make, and if you eant them to end at a specific color, you have to do a lot of calculation in your head.