Remember: the Kaggath combatants are at their height of power. So whenever the SE controlled the most land, that'd be the structure they enter the Kaggath with.
You're right, it was a slopy attack on the SE's part. But we've seen many armies in Star Wars do the same. We've also seen briliant attacks on the SE's part though.... like the one with which they conquered a nice piece of the galaxy at the begining of the Great Galactic War. Master Gnost-Dural himself stated it was briliant.
But I need not defend the SE in this since. After all: the GE was beated in a battle with Ewoks....
It's not really the height of their power, though, if they are over-extended as much as they clearly were. If the Republic of the TOR era could counter-attack and take those systems, the GE would steamroll them.