No, 12" S9 is not that good. But S9 in a multiple CC where you can re-roll your saves, Yriel kill a squad MEQs on its own and Erldrad and the warlocks take on dreads, tanks and other troops nearby is perfect. They even kill DPs with ease and all MCs with an armour save of 3+. Against those 2+ beasts you have Eldrad and Yriel as the duo of doom. Just soften up your opponent with a bit Fire Prism fire and take on its weaker rear / side with the Warp Spiders or possibly with War Walkers ...
If you go first, he has to shoot down the fortunes WS of the council. If he succeeds, he wants to get rid of it - which is only possible in CC as shooting of all units is simultaneous, so he can not kill the WS and then the council within.
In my turn, Eldrad fortunes Yriel who will bomb away a doomed Squad, and Eldrad and his fortuned council take on whatever they can reach in a multiple CC.
This busies your opponent so much, that you are relativle free to use your Prisms, Dragons, Spiders, and whatever else is included in your list. Yust ensure that your valuable troops are concealed from harm.
Tonight i will use:
Eldrad, Yriel, 8 warlocks (enhance, embolden) in WS with stones and Shuricans
2x5 Dragons in serpent as above
5 Avengers in serpent with stones and BLs
2x3 Jetbike squads
6 Warp spiders with exrch and dual spinner
2 Prisms with holo fields and stones
2 Walkers with Scatter lasers
I will go against the new Wolves and i will report ...