Well I don't have any statistics on how long civilizations last. It's true that DA is a very naive way of estimating, but I think at this time all we can make are very naive estimates.

I think that when I add other information, like my belief in x-risk, the estimates get even worse. It really does feel like our civilization is at it's peak and it's all downhill from here. Between how many dangerous technologies we invent, to how much finite resources we are using up, the estimates given by DA certainly feel plausible.