No arguments there. And like I said earlier, I'm not saying that an escape scenario won't happen here. It very well could.
My point is that whatever ultimately happens here, it will probably be a step out of the ordinary. But I could be wrong! We'll see.
Is it really a waste of time on Oda's part if Saturn fails to secure everything from Egghead Island for the WG? If anything, that sort of defeat would actually serve to fulfill the idea that "the Egghead Incident" is a shocking moment in history that has global ramifications, even if The Mother Flame and Seraphim aren't actually destroyed.
If say Saturn secures most of the Mother Flame, but one of the surviving Vegapunks manages to escape the island with a pivotal part to make the weapon even work, that isn't a waste of everyone's time- that's just fueling higher stakes between the Straw Hats and the WG into the story moving forward.
As for the Seraphim, I doubt they get destroyed, but I also wouldn't be shocked if something happens that results in them being freed from the WG's control.