Yegr, read my arguments. Plus, in the slavetaking department and the mental state of Archon's or Haemonculi a battleship is more warranted in a Dark Eldar fleet then in a Corsair fleet.
Yes I did. And I can see nothing that would stand in relation to my reservations - I still don't see a reason for them using a battleship. The DE are practically the only race in wh40k universe that can pick their battles where and when they like. They attack where they can find easy prey.
What would they need a battleship for?
I'm not questioning it would be good for them to have one, but so would be more torpedoes for chaos, more shields for space marine vessels etc. But there isn't much in way of fluff that I can see, that would lead in this direction.
As for the argument about a BB being a result of some DE megalomania: building a ship of this size requires not only mental illness (what you suggest), but also power- power that comes form some sort of cunning, treachery etc.
A Archon who use much of his/her's power to construct such a ship would most likely be betrayed and killed along the way. There is a fine line between being paranoid and alive, and completely mad and soon to be dead.
A Heamonculi should be a figure behind building a DE BB? - that's not really in his'/her's type of interests.