Besides investing in bitcoin, I am still using bitcoin to transfer money and make payments to some overseas customers and services, so is he correct in saying that bitcoin is only used for speculative purposes?

Bitcoin was not created to be a speculative asset, but we turned it into a speculative asset. So clearly you and he are wrong in saying that bitcoin doesn't serve any mainstream purpose. It was our behavior and usage that distorted the original concept of bitcoin's creation and now we blame it, LOL.

What is Bitcoin and what it can do, we need evaluation from the world community. None of us have the right to judge anything about it, you or that guy or I don't represent other people or this world. So what you say is just a representation of you and there is no guarantee that you are right and the rest of the world is wrong.