I'm assuming he's missing a listing of a spiritseer upgrade on the warlock. 10 + a spiritseer-lock makes the wraithguard troops. I've recently started mixing in this ally unit with my foot based list. I've been revolving around the wraithguard and 6-10 grotesques, a sort of life and death coven list, though it's usually 1750 so a bit more wiggle room.
The fortuned wraithguard are a really tough unit to kill, but then you invest alot of points into making that single unit/detatchment hard to kill. If you opt for book powers on the farseer, he could potentially buff the wyches as well, (cover saves, invulns, rerolls in CC.) I think that will be the important thing if you want to be using 15 wyches on foot, they will need all the support they can get. You might be able to mitigate that some by splitting into 2 squads in raiders(or a Tantalus if your local group is ok with FW). But I'll assume you are set on wyches on foot.
I don't quite know how the army is supposed to synergize, so I'll relate what I try and do with my core units. The goal is to try and get the big tough units across the table to threaten the opponents objective in their deployment zone. Ideally on a flank, this is usually preceded by a fast moving harassment unit trying to penetrate deep on the other flank (beasts and reavers work well for this, both can be fairly durable and fast).
I think that is the missing component here, all the units outside the core wyches and wraithguard don't draw any fire, and even if they did, they aren't durable enough to take much. The Venom/blasterborn and Raider/Warriors are both mid-range, so will probably advance just ahead of the core? That means they will be fairly easily focused down. If they can manage any shots on the wyches outside of cover, they will all be dead pretty quick. Leaving your opponent only having to deal with a Razorwing, Ravager, the the Wraithguard/IC group to deal with.