First, don't listen to him.
Second, against Eldar... you can expect:
Starcannons on Vypers
Starcannons on Wave Serpents
Starcannons with Guardians
Wraithlord... with Starcannon...
'Least that's what I see a lot of.
Against Starcannons... use Venom Cannons, perhaps on Warriors with Wings so they can move fast and Deep Strike. At the very least, you'll make them pay a few extra points for a Crystal Targeting Matrix.
Scorpions... there are two ways of dealing with Scorpions:
1. Get a Tyrant or 'fex in there.
2. Mob 'em!
DO NOT go point-for-point with them with anything besides Ripper Swarms, a Tyrant, a 'fex, or a CC Warrior.
Swooping Hawks... unless you want to try to chase them down, there's not a whole lot you can do... if they Deep Strike:
1. Hope they scatter bad: off the table, or too far toward your lines.
2. Watch out if you have Hive Nodes. They are easy targets for Grenade Packs... Biovores take note, too, though they have two Wounds.
Guardians: Frag Mines. Or you can run them down with fast Gaunts.
Wraithlord: Get a fair sized brood of Genestealers in: every 6 you roll to wound wounds it and denies the armor save.
As for Dark Reapers: 5 Dark Reapers, 10 shots, about 7 hits, about 6 wounds on Gaunts a turn. Cost: Nearly 200, if no Exarch.