bun seems great and promising but I'm in the same boat. vite/esbuild with vitest is running perfectly, and already fast enough (and at last not struggling with webpack or rollup overall poor quality anymore...).
My problem with “Vite is good enough” and “Vitest is good enough” as a paired hypothesis is they are literally opposite in their target environments. It’s explicitly unsupported to use Vite to build projects specifically for Node as a target, and it’s explicitly unsupported to test in Vitest in browser environments (though I think that’s being actively addressed, but it’s still going to be a second class solution).
It depends of what you mean by browser environments (integration tests?), but vitest with happy-dom is working great for testing libraries and components.
bun can run vite prod build at least and seems about 10% faster at it than node according to my testing.