There's no indication of a blitz at all. They're specifically stated to be able to retreat. And it all happens offscreen, which certainly doesn't help for any attempt to say how impressive it's supposed to be.
Not to mention, I can't recall any indication of their size whatsoever. The Gargantua sure wasn't Star Destroyer sized, and that was their flagship.
I mean, it shows that Laharl can destroy ships...of unclear size, power, durability and just plain capacity.
...Yeah, he's better off sticking to his Veldime busting feat.