When Piccolo Sr. wished for eternal youth and destroyed the dragon, Kami not only recreated Shenron, but he recreated the moon.
So, the dragon ball's creator can perform dragon feats by himself?
Or, if he simply cheated the restriction of one wish a yeah why even keep the restriction?
For that matter, remember when New Namek claimed they "powered up" Poruga? Why didn't anyone think of doing that sooner? Why keep the dragon in a depowered state at all?
And why didn't Earth's dragon get a power up?