> Next pushes towards serverless functions and API routes that I didn't really enjoy using for more than just a trivial endpoint.

By default (through `next start`) Next.js uses a Node.js server. You don't need to use Next.js serverless: https://nextjs.org/docs/deployment#self-hosting

Most large applications don't use API Routes for large workloads. These teams likely have a completely separate backend/API, and Next.js is the connecting piece for their frontend. For smaller teams, or solo devs, it's more common to see their entire backend built with API Routes (most commonly used with something like Prisma): https://github.com/vercel/nextjs-subscription-payments