I can't agree with this. No scientist says, "we know it's real because computer models but due to a fluke there's no dark matter in the solar system so we can't detect it." No scientist says, "we know it's real..." about anything. What scientists say is something like, "so far this theory has not been ruled out by evidence." So far, the theory of Dark Matter has not yet been ruled out by numerous attempts to do so along multiple independents lines of observational evidence:

- galaxy rotation curves

- galaxy cluster dynamics

- gravitational lensing

- the Cosmic Microwave Background radiation

- large-scale structure

- Baryon Acoustic Oscillations

- X-ray emission in galaxy clusters

- galaxy cluster collisions

- mass-to-light ratios

That's a tall order for any competing theories. They're welcome to try, of course, but so far none have succeeded.