I think the massive ecosystem has fewer high quality libraries than Rust at this point. I use both JS/TS in frontend and Rust (either frontend more as a hobby and backend) extensively, and I very often check the dependencies-source, and even more often rewrite it (unfortunately not in Rust), because of low-quality. And it's sooo slow... the tooling and the frontend (albeit I think that has a very lot to do with next.js... and with how easy it is to make it slow for someone not that experienced or someone not being extremely careful).

Frontend is not yet as matured as JS/TS (whatever matured is, but the count of frontend frameworks is at least a magnitude higher in JS/TS), but I think when I would start a new company I would default to Rust now as frontend indeed, the language itself is for me reason. And I think vanilla-js (or Rust?) is not that much worse (time/effort-wise, sanity etc.) for more complex applications than what the Next.js ecosystem has produced so far.