If the complaint about dependency injection is that it’s magic, brittle, and difficult to debug - globals mutation via init() is much worse. In FX codebases this is heavily discouraged. The concepts of constructors and lifecycle hooks in an FX graph are not that hard to grok; you can pretty readily figure out what’s going on if you want to.
The “import _” approach you recommend is idiomatic Go but it is inherently a global mutable state approach and not a DI approach.
I suppose elegance is in the eye of the beholder. FX is very elegant in my opinion: just specify your constructors and your needs, let the computer do the topo sort. But you’re right it is not idiomatic Go. Idiomatic Go is always to maximize the volume of rote, low-information-density code to accomplish any given task. Any time you are being clever and automating grunt work you are certainly violating the spirit of Go.