This is absolutely par for the course for Stephenson. He's written at least 4 books like this, as far as I can tell.

Seveneves in particular is 700 pages of incredible, next-level worldbuilding, then the potential for 3 more 300+ page volumes compressed into 180 pages. It's like at the 700 page mark the "wrap it up" light comes on, and he hastily bookends it.