I think that what it ultimately comes down to is empathy. What determines how smooth and effective a line of communication is.

Why most people tend to feel 'exhausted' when communicating synchronously online is that it's usually not very synced at all (interruptions both online and off are constant). So makes empathy more difficult to cultivate.

Async communication does seem to have more of an advantage here, as it is by definition a more thoughtful style of correspondence (writing a tutorial for example). And ironically, is a more synced style of communication, when the information passed on is actually being consumed.

I touched on this, and the ways in which async communications can be made to be even more effective in a recent post on my blog: "Why Most Programming Tutorials Are So Hard To Understand – (And A Solution To This Problem)" - https://fromtoschool.com/why-most-programming-tutorials-are-....