As a DEldar player I recommend allied Wave Serpents!
Nah in all serious, I like Razorwings. I like to run mine with Dark Lances for anti-Flyers as well, but if you specifically need anti-
FMC then Disintegrator and Splinter Cannon work well. They also have missiles for anti-horde.
Another thing that I like using is 10x Warriors in a Raider w/ Splinter Racks. Although they snapfire, they average 2.944 wounds in rapid fire range - nearly enough to statistically take off a hull point.
Going first will help, especially when they are grounded. In the case of Flyrants, I would try and remove the Venom/Malanthrope before you fire into the Flyrant. 2+ cover is harder to get through than 3+ armour if you're not using
WS.