If we follow normal thinking, then the heights are definitely something we ought to occupy.
But Horn knows he wants far more than a simple victory; he wants a victory so crushing that he's willing to accept heavier casualties on his own side to completely break the enemy.
Seizing the heights is fine in itself, but it will inevitably push the enemy into a conservative deployment.
Simple logic: when your odds of winning are high, you play aggressively; when they're low, you play conservatively. That makes it harder to lure Serafe out.
Besides, the Royal Court still has those breakthrough tools, the flesh-and-blood Titans and the zombie sea.
Horn does have ways to deal with them, but he can't be facing full-on assaults from three directions.
He needs a situation where Serafe finds it hard to escape, and that means using Holy Grail Heights as the battlefield won't work.
