Sounds like gaming addiction escapes him from his real demons. The games comfort and soothe him. Taking them away doesn't address the underlying issues that make him unhappy but would take away his way of coping.

At most, which is not necessarily "at best", you can take away his way of dealing with pain but he will still have to deal with his pain somehow. So he may then substitute other addictions for gaming. These may be equally or more destructive, because what's destructive is not the gaming itself but the tangle of unresolved issues driving gaming to extremes.

Sounds like a ton of consistent long-term support is needed to identify those issues and develop alternative coping/support methods before he can begin to wean off gaming. From what you've said, the things that help him are therapy and quality time with loved ones. These supports aren't there in as sustainable and consistent fashion as gaming, which is why he games. Not saying the gaming isn't a problem, but even if you successfully crusaded against gaming in his life, it might be at the cost of alienating him without really solving the issue in a way that doesn't just resurface in another form later.

His birds have left the nest so he's in touch with his online friends that aren't constantly trying to change him, criticize him, poke his wounds. You may see pointless leaderboards but he may see something fun to do with online friends that give him something his real life connections aren't e.g. maybe consistent, non-judgmental, companionship. Like people raiding WoW for the companionship rather than the loot. Or visiting pointless subreddits during down time.

By the way I'm not an expert on anything and am not talking from any kind of authority. Just sharing my read of your tale as you told it.