GPU instancing reduces FPS

I'm trying to get GPU instancing to actually benefit my project, but so far it doesn't seem to make any difference. If anything, it's making matters worse!

I've set up this very simple test case, where I have 3 different materials (with instancing enabled) applied on a ton of identical spheres. Shouldn't this be a dream scenario for instancing? And yet, not only doesn't instancing improve performance, it actually makes it worse!

The scene with instancing:


The same scene without instancing:


I've tried this in Unity 2018.3, 2018.4.9 and 2019.2.6, and the result is the same in every installation.

Is there something I'm missing here? What am I doing wrong?

Attached unitypackage.

 

Well, I submitted a bug report.
#1186742