For me personally, I much prefer SvelteKit's routing/state management over React Router/Navigation and Redux. Reactive UI to accompany ThreeJS scenes is probably just as easy in both Threlte and R3F, though I would again prefer Svelte's slot props for composability. This project in particular (from what I can tell) was showcasing V6's new Plugin system, and using their `@threlte/extras` library along with the Rapier plugin. R3F is much better in that regard, with a larger ecosystem, but it's exciting to see Threlte get closer to parity with R3F and Drei's R3F libraries; I'll likely choose Threlte over R3F now if there isn't anything from the React/R3F ecosystem I need.
Disclaimer: I use React/React Native for the frontend at work, SvelteKit for quick prototypes, and R3F or vanilla ThreeJS when playing with 3D in the web. My days of working in ThreeJS for contracted work were long before R3F or even Svelte itself was a thing.
what are they, in your words?