Next.js is infuriating

They're trying to do something that's fundamentally very hard. Unifying server-side and client-side code was always going to cause confusion when the difference becomes relevant.

Personally I'd rather go in the direction of having code that's explicitly server-side, explicitly client-side, or explicitly shared utilities. But you'd need more of a type-safe mentality to take that approach, and you'd probably scare off the majority who prefer runtime errors over build-time errors.

Your observations apply generally. Debugging "magic" frameworks is often more complex than starting with simple basics and a coherent design. As a bonus there are less dependencies, less build issues and lighter pages or binaries.