If a person has decided that phpbb is better for him, then this is normal. But how does it feel to use an outdated SOFTWARE frozen 10 years ago. The essence of the forum is not even in appearance (central page). It’s like a wrapper, you can put on any wrapper. The essence of the forum is, first of all, the possibility of communication and discussion. The functionality of the discussion and comparison of Discourse and phpBB does not make sense.
You can really show him examples of various forums used by Discourse. But if he wants to stay on what he has, that’s his choice.
He is pleased, but are you pleased? Maybe you should create your own forum? 