Yep this is what's often misunderstood.

We also recently cut our build times in half moving from Webpack to Turbopack on production builds after jumping to NextJS 16. We'd already been using Turbopack in development for a while which yielded massive DX improvements related to performance. Production build times will drop further once Turbopack production build caching is stable.

Webpack -> Turbopack is the smart initial migration. I'd bet Railway went straight from Webpack -> Vite not realising that their real gains sat with the build tooling, not NextJS vs Tanstack.

Yes I'm on turbopack and running the latest version of Nextjs.