The Arc GIS terrain tiles are slower because it produces significantly more geometry. You can see this by turning on the Cesium inspector:
viewer.extend(Cesium.viewerCesiumInspectorMixin);
``
And then clicking Terrain > Wireframe. Notice the Arc GIS terrain is much more dense, because it’s created from a height map, as opposed to the quantized mesh format which allows you to have highly detailed geometry without requiring a regular grid.
We are always working on improving the accuracy and quality of Cesium World Terrain - are there any particular areas you’d like to see improved?
Just to update this thread, part of the reason the ArcGIS terrain is slow here is because the Globe picking (which is used when the camera moves to make sure the camera doesn’t go under terrain)is a bottleneck. There’s an issue for this here: https://github.com/AnalyticalGraphicsInc/cesium/issues/8481
You may be able to get better performance by turning off the camera collision detection: