That's very true, asynchronous isn't a fair way to describe things.

But given a hint about their level of presence, what are you doing with that information? What can you do after sending the message you were already going to send? Worst case it makes people send "???" as a follow up because they can see I'm coherent enough to tap a notification and assume that means I'm available for a full conversation. The opposite example is the typing indicator, which acts as a useful mechanism to keep a conversation ordered and flowing once it's started. Maybe an argument could be made for the "currently viewing" indicator being more useful, since it solves the problem of indicating I'm available for a conversation better than just "read y/n".