Well, you got a reply and they gave you a time period. I'd be inclined to wait and see what happens in that period. It's not as if you're waiting on something life-changing or which you must have this week right now in your hand or else...
Flight delays happen. Presumably they were "out of our control" or you'd have filed for/been given EU compensation already, in which case I'd say you're basically likely to get a response stating "sorry, these things happen". And maybe some duty free vouchers as a gesture of goodwill. I wouldn't hold out much hope for much compensation - sh!t happens as they say. But if you're lucky, you'll get that and a more detailed, personal reply which lists the circumstances and reasons (which, personally, is what I'd value more highly than some vouchers just out of curiosity).
Also, if you're thinking of "bouncing this back" to BA at the moment, I'd advise against it - they have far more important things to worry about (and complaints/rebookings for far worse delays) right now. I'd imagine such a "bounce" would go to a queue and not yield much for the 6-8 weeks anyway whilst the current mess continues.
I say, wait it out and give GB a chance to deliver a reply within the stated period - if they do, good for them for being accurate (even if you think it's a bit long personally). If they don't, you'd have cause to complain again more vociferously.