Civil War is not insurgency
I'm not sure I agree.
Nor do I
Nor do I... but once again, and not for the first time, discussion founders for want of a consensus definition of what "insurgency" actually is. Given the amount of discussion devoted to it, you'd think we'd have sorted that out by now.

Personally, I'd say the most basic definition of insurgency would involve intra-state armed conflict between an acknowledged government and an organized populace or substantial portion thereof. I'm sure that could be picked apart, but it's a start.

By that standard the US Civil War qualify as insurgency. I'm mot at all sure the Afghan conflict would. The question, really, is how Afghans define the conflict. If they see it as the Taliban fighting the Karzai administration, with the US supporting the Karzai administration, then yes, it's insurgency and the ability of the Karzai Government to provide adequate governance is a key factor. if the Afghans perceive the core conflict to be the Taliban vs the US, then we no longer have an intra-state conflict,and the ability of the Karzai administration to govern becomes a matter of secondary importance.

What is the conflict about, at base? Are the Taliban fighting the Karzai administration because they think it governs badly, or are they fighting the US because they don't want foreigners in their country and they won't accept a government installed by foreigners no matter how it governs?

Brought down to lowest terms, is this fight about the Karzai Government, or is it about our presence?