Bah, you're right, I knew it was odd it didn't seem as terrible as I remembered it.
Misread twin linked.
Well, against AV10 (Dakkajets, Razorwing, Ravens & a few others)
2 BS4 S8 bright lances: 1.32 hits/.99 glance-penetrating hits/-.66 HPs with 5+ jink save
6 BS4 S6 shuriken cannons: 4 hits/2 glance-penetrating hits/-1.33 HPs with 5+ jink save
Not bad, pity every flyer bar the Lightning, Barracuda, Hell blade and Attak jet has 3 HPS.
But compare to a vendetta with two heavy bolter sponsons, five points less than the Nightwing and lacks vector dancer but is going to get at least one auto-glance from the lascannons with the re-roll and will average two more glances from the heavy bolters. Edit: Oops, forgot saves for the Nightwing, it reduces the amount of HP lost quite a bit but still doesn't make the Nighting any better at killing flyers. It is AV12 as well so for a Nightwing it is:
2 BS4 S8 bright lances: 1.32 hits/.66 glance-penetrating hits/-.44HPs with 5+ jink save
6 BS4 S6 shuriken cannons: 4 hits/.66 glance-penetrating hits/-.44HPs with 5+ jink save.
So if a vendetta gets a shot with its weapons it will almost certainly destroy the nightwing (even if it just gets one sponson in LOS it has a fair chance of doing this. In contrast a Nightwing will probably only take one hull point from the vendetta.