The only thing that makes it "sci fi" is the alien and the time travel, and that is marginal. The plot is a basic military/revenge plot:
An renegade military naval leader steals a warship. The warship has an surface battle with a warship from an international alliance.
Then the renegate naval leader shoots a nuclear missile at a city and destroys it.
The international alliance sends their own warship out to stop him. They use superior speed, conventional weapons, planes, and the help of one of his former officers to aid themselves in stopping him by making him target himself with another nuclear missile.
With that reasoning none of Star Trek would be considered scifi.
"Oh that's not scifi, that's just wagon train to the stars."
You could do that with Wrath of Khan, or BSG, or Star Wars, or hell anything scifi.
IMO, I suspect what we have here are some people who are angry this movie isn't like TMP, and doesn't lead into TOS, and therefore have decided beforehand to find reasons to hate it.