> And, async doesn’t have to be lower-bandwidth. With even a modicum of planning, engineers can be set up to pick up the next most important thing if they’re blocked waiting on a response from someone else.

Sometimes! The hidden assumptions are that you have a backlog of independent tasks to pick up, and that most dependencies are well-defined enough that there's no need for a back-and-forth to understand the problem. I don't think those are crazy assumptions, but in the kind of company the author is running (a startup building new stuff trying to find product/market fit), neither is typically going to hold.