I'll throw my two cents in as well. I too was skeptical about Seekers. I chose them for no other reason than I liked their fluff piece the best.
Played my first game of AoS2 slaanesh the other day as seekers and I crushed it. I'd say daemonettes and seekers of slaanesh are going to be your problem units, as even if you advance them they can still charge. With the daemonettes I just tried to stack my odds in getting the charge off first (which I've found essential in AoS). I deployed them a little farther back than I usually would and relied on their high movement and a token speed bump unit to setup the charge. As for seekers of slaanesh, I had good success rocketing them into flank units I could overpower, then spring boarding them deep into soft targets in the back-line on the following turn.
I very much enjoyed the depravity system. In the past I was always hesitant to throw my heroes into the fray for fear of losing them. Now its like some mental block has been lifted. I just started throwing them recklessly into the enemy and it worked out pretty good this time. It was a thousand point game and I pretty comfortably hit 18 depravity points.
If anyone was curious I used a Keeper of Secrets, Herald on Seeker Chariot, The Masque, 30 Daemonettes, 10 Daemonettes, 5 Seekers, and the Malevolent Maelstrom. My opponent played undead using a Wight King, Tomb Banshee, Necromancer, 2x5 Grave Guards, 40 Zombies, Corpse Cart, 3 Vargheists, and...Suffocating Gravetide?