while I agree that giving it the ability to summon the avatar is a needless buff, one of the few arguments against the eldar basically getting a free greater daemon is that you need farseers or equivalent to summon it, having a very tough, DC6 fearless war engine as a backup really means you can't stop the eldar summong the avatar by cheekily snagging all the farseers....
however I think it's about right at 850, in a 3k army that means you can't fit any air units into the list so you're relying on the ground pounders, it's also a big bite out of your points total and an army with a warlock is unlikely to have more than 10/11 activations, several of which will be relatively cheap and vulnerable, certainly not optimal for the eldar in general
a canny opponent will use scout screens to limit the movement options of the warlock and feed it cheap formations while concentrating on taking the rest of the eldar army to bits.... at DC6 it's also within the realms of possibility to break through blast markers alone, and although scant consolation, it *is* vulnerable to crossfire, something my reaver titans have found particularly painful
none of this is meant to disparage anyone, the warlock is definitely the best top-end battle titan and is almost always a better choice than a warlord titan or great gargant in other armies, I just think that in the context of the effect it has on the eldar list it's
just about okay as it is
although it definitely doesn't need to be able to summon the avatar, that's a buff the eldar list just doesn't need....
![:{[]](./images/smilies/headbang.gif "Headbang")
My point was a that when hit with a TK weapon a knights shield goes from stopping 50% damage (inv) to stopping 0% because it is completely negated by crossfire. A holofield goes from stopping 66% to stopping 50% with crossfire... Note even vaguely comparable if you are trying to argue that crossfire is a legitimate option to taking out a Warlock... 
