> Science fiction (sometimes shortened to sci-fi or SF) is a genre of speculative fiction which typically deals with imaginative and futuristic concepts such as advanced science and technology, space exploration, time travel, parallel universes, and extraterrestrial life. It has been called the "literature of ideas", and it often explores the potential consequences of scientific, social, and technological innovations.[1][2]

That definition doesn't really fit The Martian. If your headcanon definition of SciFi does include The Martian then that's fine, but I don't really understand how you think excluding it from the category is an insult when for most common definitions it doesn't really fit well.

In my mind, SciFi is Asimov's Foundation series, or Star Trek, or Dune. It's set in the future or an alternative universe with considerably different, more advanced technology than modern-day reality. The Martian is set 13 years from now, using today's technology.