A Supreme Origin god can have a power of 10. They currently might have the power of 15 due to the fusion of many Supreme powers. But a world god with the weakest world will have a power of 10 multiplied by 2.
There's no way this dragon world god has a world with an amplifcation of 2. His world was too large. It was larger than the whole Tyrant realm. The force that struck them felt more like 50 instead of 20. They were outclassed by every definition of it.
Things would have been different if they had a world to handle the repercussions of the collision. Unfortunately, they don't. It was like the backlash of the void universe all over again.
Their world fragment couldn't handle the blowback from the collision with a whole world. After all, it is just a fragment of a world. So Legion disintegrated and disappeared from the presence of the world god. Their existence in front of the world god had been denied.