First of all, normally said "singularities" are moved by the Vong crawlers themselves, so if Luke maneuvering them is wank, so is the Vong. Of course, the Vong are a wank concept, but...Master of Ossus wrote:Luke used the force to move artificial SINGULARITIES. Sorry, but that is uber wank right there.
Second, a singularity can be of very low mass. It just has to be very dense.
Three, it is not even clear those are singularities in our sense - IIRC there was some discussion about them not acting like real black holes. All we are really sure is that they are some kind of point defence that can warp nearby space.
Four, technically, Luke didn't move them. He stopped them from moving. The Vong accidentally moved them on themselves after Luke released it, kind of like how one might lose balance when in a tug-of-war if the opponent suddenly lets go of the rope.