> Next.js tightly couples your front-end and back-end, no question.

I'd question that statement, since it's wrong. There's no requirement to connect your NextJS server to your backend databases, you can have it only interact with your internal APIs which are the "real backends". You can have your NextJS server in a monorepo alongside your APIs which are standalone projects, and Next could exist solely to perform optimized payloads or to perform render caching (being the head of a headless CMS). It seems like a weird choice to make but you could also build almost a pure SPA have have Next only serve client components. The tightness of the coupling is entirely up to the implementor.