Yes that's what I thought, seems odd not to provide a specific tool to do this simple thing rather than having to trial and error adjust until your nutral reference tone is nutral - Oh well.
It’s more complicate than we would like to have it.
White balance in ACR acts on linear, non-tone-curve-treated data. At this stage, it is just a question of linear scaling (multiplication) of the single R/G/B channels. One single neutral bright gray is enough to set the eyedropper. Otherwise, while Raw conversion, RGB data and "color temperature“ get distorted and inhomogeneous along the grayscale because of application of a brightening S-shaped tone curve.
Therefore, in Photoshop it requires at least two gray patches for reference to achieve neutral white/gray. With the brighter one, the top channel should just reach 255, so that you can set this patch to R=G=B by means of the single R/G/B Levels’-highlights sliders. Next, you need a mid gray to adjust R,B to the of level of G by means of the single Levels’-midtone sliders.
In short, Photoshop can not offer a (proper) white balance tool, whereas Camera Raw can.