It's not the same, though. Chat is asynchronous, so the recipient doesn't have to wait with their device as they would on hold.
A standalone hello is actually more efficient in time-sensitive situations. The sender needs to know if the recipient is actually available so that they don't waste effort typing a question that won't get answered in time.
He explained it. Its the equivalent of calling someone for help and putting them on hold.
I think it's okay if you at least give the topic of your question or start asking it in the first line and within five seconds or so get to the point.
But if you just give a greeting or something and then delay, it wastes people's time.