Thanks for the feedback!
We did upgrade the tilesets exported from RC (which are v1.0) to 1.1, + did some draco and ktx2 compression for geometry and textures, and this resulted in way smoother loading times for 3d-tiles tilesets! The difference is really impressive for both web viewing and Unreal Engine integration via the Cesium for Unreal plugin.
Hopefully these settings can be added to RC 3D-tiles export dialog: default to 1.1, and allow for geometry/texture draco/ktx2 compression. These would be passed to gltf-transform gltf-pipeline during 3d-tiles-tools upgrade, via the options flag, see readme