Something that people don’t realize is that standard deviation in framerate trumps frame rate in perception of smoothness of animation. It’s something that NaughtyDog has blogged about, and something really well known in the Amiga demo scene.
I’ve seen 8 fps marquees that looked smooth as silk the frame rate SD was so low. It’s amazing what the brain and eye tracking will do to make things look right.
Variable refresh rate monitors don't solve hitching due to variable computation. In order to render an animation smoothly, you have to know precisely when a frame will be displayed ahead of time, so that you can render the simulation precisely at that point.
I suppose if you know UI cache of some element will be invalidated this frame you can inject a delay up to expected upper bound in frame time increase it will cause and artificially hold back next frame flip by a variable amount if it takes less than the max expected delay. It could be tricky to get that from the GPU with all the queuing it can potentially do and stuff though.
Also, battery life/power usage is an important factor that can push you away from focusing only on consistency.