I think that flakk isn't even necessary in the game, from what I've witnessed. The flyers are good but it is easy to make them overshoot their target, come down to the ground, and get merc'ed cold by tons of attacks while hovering. The vehicles that can't hover end up only really in the game for 2/3 of the turns, and only fire effectively for as little as half of that. I ignore them utterly, and so far it hasn't let me down; I take some rough volleys of fire but dealing with flyers defensively has served me well overall since their introduction. I think too many people are just obsessed with the idea that in 40k that all you can do is kill things. I am sometimes spoiled by our terrain and forget that other folks don't always have the same sort of stuff but with a good mix of terrain you can make it very annoying for a player using a flyer.
The idea that you absolutely lose all your AT before you get to shoot at the flyer is ridiculous. Heavy weapons can be hidden and step out to shoot a flyer.