It can be too slow to catch up to rapid change, but then in that case one of the things you want is a diversity of cultures for selection to act on.
Is this the problem that you are trying to solve by preserving cultures? Make the human race as a whole more resilient in the face of rapid change?
Is this really the reason why you think culture is important? Or is it a rationalization?
I am skeptical for two reasons:
Your argument about rapid change seems extremely different from your argument in the grandparent post where you talked about literature and philosophy, Aristotle and Chaucer.
Do you think that preserving a bunch of tiny cultures of a few hundred people (many of whom probably live in poverty) is really going to help make the human race more resilient in the face of rapid change?
This is a valid point. But the world is far from a monoculture. Even if all currently endangered languages die out, we will have plenty of cultures left.
If the world ends up with less than, say, 100 languages, then I agree it starts to make sense to preserve them. As it stands now, I think we have more than enough cultural diversity, and keeping tiny minority languages and cultures alive is not worth the opportunity cost.