The models _can_ do it, but you need to ask for the right things. Most people don't, they'll usually blame the browser for being slow or ugly when they can't break through the THREE demo page wall.
A larger THREE.js project starts to look more and more like a game engine, so you pick and choose the parts you need. There's a ton of open source libs, most of the heavy components the big players use are open source, things like physics, mesh optimization.
Key AI-specific parts might be:
- a harness (so the agent can drive the thing)
- authoring pipeline (so you can bake/optimize assets)
- some sort of coherent renderer architecture (what are your assets, your passes, what's your shader graph).
Without some fundamentals here you are on the short road to falling off the cliff of tech debt and the AI will gladly drive you off of it until you ask for an expensive rewrite.
> would you create models independently
Yes. Pretty much any proven gamedev/asset pipeline is something frontier models are good at. Procedural systems, asset store, free content, Blender, Meshy.
Literally anything except "make a THREE.js scene" -- which is not a technique used in gamedev, beyond throwaway prototypes or demos. Which is what you will get if you ask for a THREE.js scene.