Even if Broly spent his whole life from infancy (which isn't possible) he'd have to destroy millions of stars per day to do that based on an average sized galaxy. And upper hundreds of thousands for small galaxies. Even though that doesn't make sense (also most star systems are separated by light years). That's saying Broly travelled millions of light years and destroyed millions of stars every day for decades which is still immensely impressive. But given the fact that Tarble had Broly under control and King Kai's reaction that scenario is very unlikely. Even if you don't want to believe that Broly is a galaxy buster, he would be a multi million star buster per day at minimum. Granted it doesn't make much sense in the grand scheme of Z's power levels for Broly to have either level of power, but it is Z and it is non canon.