As founding member of TWRL (TEST Weapons Research Lab), I can tell you from a few moments of making shit up, the blades on the Vanduul ships aren't for Ship to Ship combat, they are for Air to Ground anti-infantry.
A Scythe or Glave comes in low over the battlefield, then lower, then lower, and even lower until they are only flying a few feet above the ground... then the blade comes in to play slicing their way through battalions of grunts with barely a thought - the best anti-troop Vanduul pilots can make perfect decapitation runs getting the exact average neck height of the force in front of them for the maximum amount of perfectly sliced heads for their eventual victory party,
'Duul never wash the gore of their craft, in the more hectic ground battle zones you can tell an enemy pilots skill by how red their ships are.