I'm curious to know more about their statement that loading textures in a WebWorker caused additional performance overhead versus loading them in the main thread. I have my own WebWorker based texture loading system and it is significantly better than not using it.

At the risk of stating the obvious, as OP seems pretty well on top of the Web API game, did they remember to mark the texture data ArrayBuffer or ImageBitmap as transferable?

Though, I suppose my metric is "number of dropped frames", not "total time to load" and I haven't actually measured the latter. My project is a WebXR project, so the user is wearing a VR headset, wherin dropped frames are the devil.