I have this idea that the Klingons were really set back by Nero's attack.
Didn't it look likea Klingon moon (Praxis?) was detonated before its due time?
Khan wasn't supposed to be found this early, so the timeline is rather out of sorts. Spock Prime should have ignored the temporal prime directive and mind melded with new Spock, so as to have him able to explain plot points to the audience and have a leg up.
So this universe is already accelerated by Nero's tampering--leading up to a new singularity. The Borg are found earlier.