Point cloud render performance transparent vs. opaque

The performance of rendering 3D tilesets (point clouds) is much better when rendering with a transparent style. In my case it was especially apparent with multiple point clouds rendered at the same position with a lot of overlap. (Use case: multitemporal point clouds).

My machine is a 2016 MacBook Pro with a 2GHz i5, 8 GB RAM and an Intel Iris 540 graphics card.

I could reproduce it in a sandcastle on Cesium 1.74. I basically added the point cloud 50 times to make performance critical. You can switch between opaque and transparent with the transparent variable.

My question: Do you have a good explanation for this performance difference? Is this intended? Or should the performance of the opaque rendering be better?