How about you stop discouraging him.

If he wants to use ubuntu. Let him use ubuntu. If he wants to use a better distro for gaming like arch linux he can do that too. Going all in is the way to go.

The whole point is to break the proprietary addiction.

We all start out with Ubuntu for our training wheels for Linux. Once he learns how to ride a bike and gets comfortable with it, we can move him up to riding a motorcycle when he is ready.