I see! That's really awesome - I've been working myself on making ECS/DOTS (with Jobs and Burst) work in WebGL, which was an ordeal especially because the Hybrid Renderer does not yet support WebGL so I'm using Companion GameObjects for now (with all logic applied to entities and just the transform of the GameObject synced every frame).
There were a few other gotchas if you're interested, but at this point your approach seems way more feasible (also for not using preview packages~) Good work, thank you for sharing~!