This is not how orbits work in galaxies. Every star is attracted to every other star in the galaxy. (Plus the dark matter halo, which we will ignore for now.) A SMBH can put 10,000,000 solar masses into the volume of our solar system, which is a much larger average density than the rest of galaxy. However, if pick a star at random from a galaxy of 1 trillion stars and then draw a line from my star to the central black hole and then center an arc of width 3.6 arcseconds (1/1000th the way around a full circle) on that line the arc will enclose at the very least 1/1000th of the stars in the galaxy, which for a galaxy of 1 trillion stars is 1 billion stars. The 10 million solar mass black hole then constitutes (1/100th) of the mass in the smallest possible slice which is itself only 1 of 1,000. The SMBH is such a small portion of the total mass that you could likely remove it and see minimal change in the large scale structure of the galaxy. Assumptions in my argument: Spiral galaxies can be treated as 2 dimensional disks. The average mass of a star is 1 solar mass. A spiral galaxy cut into "slices" like a pizza would have equal amounts of stars per slice.