[the8472]

> When I think of a black hole, I assume it has a gigantic mass, enough that it's always the most massive local object, and subsequently pulls in all other things.

The sun is not pulling in the earth. Earth orbits a common barycenter with the sun. That barycenter happens to be inside the sun, but the sun is also orbiting around it.

So a small object orbiting a bigger object is an approximation. Orbiting their common center of mass is a better approximation. This is more easily visible in the pluto-charon system.[0]

The same of course applies to black holes. Them being heavier than most other objects in their vincinity does not render them immobile any less than the sun being the most massive object in the solar system renders it immobile.

[0] https://en.wikipedia.org/wiki/Charon_(moon)#/media/File:Plut...