You're proposing that I should doubt either naturalness or homogeneity because a purely speculative technology is not observed.

Not just a speculative technology. Those technologies are just some examples. As noted, there's also a complete lack of radio sources. There's no sign of any sort of alien life at all. If an alien civilization arose and prospered a billion years ago in our galaxy, we'd expect to see some sign of it, such as colonizing planets. And the lack of specific speculative technologies isn't the problem, it is the lack of any sign of any sort of larescale use of the massive quantities of energy available to stars. It is all getting wasted. And that's not just true for our galaxy, every galaxy we look at looks completely natural as far as we can tell.

Of course if you are absolutely set on preserving a strong form of homogenity and the naturalness of the universe there's one obvious solution: There's a Great Filter in front of us. Things are homogenous, and species get wiped out by something, probably a technology they decide to play with. If you are convinced of homogenity and naturalness then the Great Filter should frighten you.