As a helmet light back-up to a bar light I actually prefer the Joystick. It’s got a great, focussed beam and the Exposure helmet mount sits the light far enough above the helmet that you can actually feel the relatively small difference in weight.
If I were trying to ride with a helmet light only, I’d go Diablo and ditto if I wanted to use it as an occasional back-up bar light, but for helmet use with a bright, floody bar-light, where you’re basically just filling in gaps and adding perspective, the Joystick makes more sense to me. I have both btw.
Edit: as a late summer ‘just in case’ system, a Joystick headlight together with a Diblo on the bars works pretty well for an hour or so and takes up minimal pack space, but obviously, you need both lights for that.