ACR and Lightroom HSL

It's documented that the saturation slider in Lightroom's HSL panel works like Vibrance.

This is a misunderstanding, that's not how it works. Edit: I misunderstood, I assumed you meant the global Saturation slider. The individual sliders may work differently.

You can simulate Vibrance vs. Saturation in Photoshop, with a Curves layer set to Color blend mode.

• Moving the white and black points into clipping (a steeper straight line), simulates Saturation. This drives color channels into clipping very quickly.
• An S-curve simulates Vibrance. This way you get increased saturation in the midrange only, but no additional channel clipping.

In any case, all the HSL controls should be handled with care. If overdone, they can break up image integrity with blocking and banding. Counter to what you'd think, this also applies to raw processing in Lr/ACR.

Well that would be weird in either case since there is a Saturation slider as well as a Vibrance slider. Do you know how those work differently? Saturation raises or lowers the overall saturation of the image evenly. Vibrance increases the intensity of the more muted colors across the image, while leaving the more saturated colors alone.