I gave three explanations for the people who said "he destroyed one thing at a time". The start of the destruction and the time it ended is 7sec in the vid. If someone argued it was "one by one", that means Brolly is zipping around a galaxy in a spiral formation at hundreds of trillions of times the speed of light, letting out planet, star and system-leveling blasts at ungodly speeds. Which would make him faster than anything in the DBU, and Superman too.
The 2nd would be targeting Everything in the galaxy and firing attacks at them from one location. This would mean Brolly has Cognitive powers beyond any of which any of them could imagine and his attacks would be moving at trillions of times light speed. This would give him a mental clarity on the level of Cosmic Awareness and then some. Which is Unlikely given he was under Paragus' control via the Control Circlet at the time, which kept him in a Restrained power form.
3rd he launched an attack of such force that it ripped across the whole of the galaxy, utterly annihilating it. The destructive force moving faster than the initial attack. Which makes the most sense. Basically like a huge bomb going off in the center of the galaxy and spreading outward. Which is pretty much what we see happening.
So, it comes down to Brolly either possessing speed enough to make Flash, the Runner and the Surfer blush with embarrassment, or he's a galaxy buster in a restricted form.