So, a certain thing's been on my mind lately... Specifically, about DBZ; and why Buu is stronger than the five Kaio-shins.

The theory as to why this is, is... Buu was the first Hakaishin. The being/force that made the Dragon Ball universe made it so the forces of life; the Kaio-shins; would be weaker than the Hakaishins, so that they would not be able to stop the cycle of life and death; of creation and destruction. And the Hakaishins wouldn't WANT to destroy the weaker kaio-shins; or they'd eventually run out of things to destroy.

As Ichirō Ōkouchi once said; “Before creation there must be destruction. If my soul stands in the way, then I'll toss it aside. Yes, I have no choice but to move forward.”

ANYWAYS! It could be that Buu was TOO destructive, ending life and worlds at a FAR greater rate than shin-jin could create it; leading to the first group of Kaio-shins and/or the second Hakaishin sealing Buu into his hibernation cycle; and possibly banished a good portion of his power (Which would explain how much stronger Beerus is than Buu). Buu being too destructive a destruction god would easily explain why there are only FOUR galaxies in the Dragon Ball universe; compared to the billions in our own.