The Gradient Ramp works fine for me.
Max's Gradient Ramp useless in creation complex material with Arnold's shaders because Max's maps not compatibility with Arnold shaders. We need Arnold's gradient ramp!
As Lee said, the gradient ramp works fine. You just need to enable the switch which he shows on the right side of the screenshot "Legacy"
I added Idea about Ramp shader, please vote if you need it too:
https://forums.autodesk.com/t5/3ds-max-ideas/arnold-ramp-gradient/idi-p/7629332
ramp_rgb and ramp_float work perfectly in Houdini and cinema4D. You can unhide them in mtd file, but they are unusable in Maya softimage and 3dsmax.