How much of it was the UI, and how much of was the non-ux code? Could've you achieved many of the same gains by creating a local backend in rust for things like indexing and leaving the UI as a more lightweight electron app while saving a lot more time in a rewrite? How much dev time was the UX rewrite compared to the backend rewrite?

The UX was a small part of the re-write. Since we started from scratch we had a blank slate and figured we'd go all in on Tauri/Rust/React vs. trying continue with Electron in the mix.