[kelnos]

I think you are perhaps not aware of how people use messaging apps in the real world. Many people (myself included, sometimes) will break sentences or sentence fragments into different messages. If the messages are displayed out of order on the recipient's side, it would be pretty hard to understand.

And even in the case where people do tend to send one complete thought per message, it still matters: like maybe I send a message, and then have an extra thought, and send a follow-up message that clarifies my first message. If they are displayed out of order, that will be confusing.

Even if two messages are completely unrelated and completely separate thoughts (honestly this feels like a much less common case than the alternative), messages just should be displayed in the order they were sent, because that's what reflects reality best.