I could explain how that's not a good reason, but I will leave it at that.
They also don't let you enter the area where the Star of Darkness is before you seal it, and if they had done so, players would just attack & shoot it (which would do nothing) and ask themselves "wait can't I just kill this thing before it becomes a threat? And then the idea would pop up in their minds as he revives. So yes, it would have been wise to destroy it prematurely, it's weaker, it's present here unlike with the Jamba Heart situation. You tell the Starries and then that's it, they no longer need to waste their life sealing that being after it's annihilated.
(Now sure, you can argue the characters are dumb, but that's an excuse, the point is that the story should have been written in such a way that the dumb characters' actions form part of events that make sense without such a clear, easier alternative. You wanna say "go get them [X dumb character]," without the understanding that this isn't the best course of action, imagine that story that does that vs a story that doesn't do that.)
I think they want to revive Meteonelfilis good like with Void, but, not really, they just want to seal it. So why was it they were talking about reviving him good? Am I missing something? Was it a misdirection so that we wouldn't think about destroying him prematurely?
Bc of this, my headcanon is that you could enter the area where the Star of Darkness was at first, and then they removed it bc they understood the issue it brings, yet didn't fix the issue. You can try to enter the place before the end of the story, which will make you see the issue, and there is an animation of you entering, but the game prevents you from being there.
And then Meteonelfilis revives anyway while fully sealed again, I have issues with this as well. It's not like the heroes did something wrong or the villain outplayed them, this is the lamer option. Imagine you collect X to prevent X on a villain, and you see the villain, you imagine something's going to go wrong but don't know what. You collect all of X, the villain just overpowers whatever you were doing and it was all for nothing... Really? That's it? Say, remember when Hyness couldn't 100% fill the Jamba Heart 'cause we stopped him in time, so he sacrificed his generals and himself to fill the little that was left? That was great, this is lame. I don't care how the Star of Darkness gets to have "Resistance to Sealing" with 2 examples present in-game.
The Star of Darkness was falling on this world already breaking away from the sealing, stood in one place doing nothing, got re-sealed again over time, and then broke free and revived, so... was it already able to break free and was only charging power to revive? I imagine it cannot move as the Star of Darkness, otherwise why stay where they're sealing you, yet it can break free of the sealing and create creatures to fight Kirby. That comes off as convenient; he can do this & that but not move, and of course it can't 'cause if it could we would see it try to escape and kill it. The villain relies on the Starries being dumb and not telling the heroes, "Hey, this guy broke free from our sealing once, let's do something to fortify it once we re-seal him again. Otherwise he might just break free again, imagine that."
Meteonelfilis is the lamest modern Kirby main antagonist, all his actions are basic within his own abilities. Everyone else is better than him, they're either way smarter or have better written reasons to be dumb or act via simple actions: Magolor, Taranza, Sectonia, Susie, Haltmann, Star Dream, Dream Kingdom Taranza, Dark Taranza, King D-Mind, the Mage-Sisters, Hyness, Void Termina, Parallel Nightmare, Galacta Knight, Fecto Elfilis, and the Master Crown. Meteonelfilis only has spectacle and his connection to Elfilis.