> There's a lot of what I'd consider to be non-trivial transformation going on between the code you pass to the Svelte compiler and what comes out of it and runs in the browser. Personally, I'm less comfortable with that compared to React's runtime library approach.

I initially had a similar concern, but so far, the opposite appears to be true. The Svelte compiled code is quite readable and easy to follow, and because there is no runtime, it's much easier to walk through exactly what is happening. With a complex runtime, it can sometimes be difficult to figure why something isn't working as expected without having a deep understanding of the runtime codebase.