Well, at least, not the only destroyer of the worlds. I have lots of reasons why Galacta Knight is the true destroyer of the worlds.
Galacta Knight is known as the strongest warrior in the galaxy.
It was mentioned that Galacta Knight could destroy a planet or two with ease.
He defeated Star Dream!
He could be the future version of Kirby.
He broke himself out of his seal in one Kirby game.
Why does everyone think Void Termina is more powerful than him?
Void Termina seems to take time to destroy a planet.
He's faster than Void (maybe).
We don't know about Galacta Knight's backstory that much. All we know that he was SEALED AWAY BECAUSE OF HIS POWER. Indicating how strong he was.
He's the true destroyer of the worlds.