I can appreciate that they are different tools, but to accept your challenge, I submit three.js, along with the multiple websites that have boatloads of single feature demos. In the particular venue of 3D graphics in the browser, I contend three.js would provide more depth than anvil's breadth.
That being said, I see no reason why you couldn't combine the two, and get the best of both worlds.
> I see no reason why you couldn't combine the two
You bet! Although Anvil mostly shields you from the mudbath of the modern web front end, we do have full HTML and JS interop. So you can call into JS from Anvil's Python code, and into Python from JS.
Even better, once you've built your (eg) three.js interface, you can package it up as a custom component. Then you (or anyone else) can drag-and-drop it onto their page and use it with a pure Python API.
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I haven't finished editing the tutorial video for this, so I'm afraid I'm just going to point you at the reference docs.
That being said, I see no reason why you couldn't combine the two, and get the best of both worlds.