Lets face it, Razorwing is a crap dogfighter. 2 Lances, even at full BS is just 2 lances. They can miss, they can roll bad on damage table. And those same Vendettas will screw it 90% of the time. So, why bother with AA role at all? And its not even with us at turn 1, so AV damage from those lances are not that important.
It is, however, a good infantry killer, why not stick it to its role? It maybe crap dogfighter, but its really good at staying alive to the rest of the game, and at the end of the game there is some things needed to be done like kill those enemy troops, destroy clumped up squad etc. Thats where its good it, and thats well actually the reason to take it at all.
My advice - dont take lances, if you wanna have meaningfull AA take Voidraven. Lance Razorwing is a trap.