Keep in mind that the Option A has a Def-line. When deployed in my table half (i.e. beyond my deployment zone) scarabs cannot be seen at all for the first 2 turns. By then I will have added 6 more scarabs to 1 unit, or 3 to each (from the Spyders).
As to Whip coils, I find that they are only good after pile-in moves. Usually I only get 1-2 models affected on my charge. Worse still is the fact that you need the Whips in front, where they tend to die first.
The casters also make more use of the D-lords Preferred Enemy rule. I would rather have the 6 Casters than 3 Whips for the points, but that is in casual games. Although I have given thought to dropping the casters for 2 Whip coils just for Tournament play.
In answer to you question about Flyers, I don't see alot of horde-style lists in my local area and my typically 2000pt lists always use 5 Flyers to great effect. In the end I only have to leave combat airspace with 1-2 flyers a turn, leaving me with about 4 on the table at any given turn.
My goal with this list is to target denial. My opponent will not see anything turn 1 (or it will have a 2+ cover). Once Night fight goes away (hopefully not before turn 3), most of my flyers will have come in, and between them and the Lightning, crippled my opponent before any resistance can be mustered. Then it is an easy matter of cleaning up the remains with more Flyer shooting and CC. By turn 5 I should be able to deploy my Troops on objectives with no threats nearby.
I think I am leaning towards option B, though.