Why is Janeway's return from death not the stuff of science fiction? Do you not accept that David Mack's Caeliar were science fiction? You might not appreciate the "return from death" plot line, or like me hate the over use of "interesting and loved character death" as a plot line, but that doesn't mean Janeway's return isn't science fiction.
I'm not here to argue simple plot devices because it comes down to a matter of taste, but what makes up "science fiction" is pure speculation. It is all about world building and Star Trek is already in the division that uses "back from the dead plot lines," and they have been for years.
While I am sorry that you cannot appreciate "living" Janeway as much as a lot of us do, I am certainly very glad Kirsten Beyer brought her back and I think the way she did it is not only good science fiction, and good world building, but fits to standard Star Trek canon.