For live service games, self-hosting is increasingly uncommon. During the Source era of Team Fortress 2, Half-Life Deathmatch, etc, self-hosting was certainly a

For live service games, self-hosting is increasingly uncommon. During the Source era of Team Fortress 2, Half-Life Deathmatch, etc, self-hosting was certainly a thing. But in the modern era, games like Overwatch 2 have no means to be a server or listen server. Even "custom games" where you can make your own game mode and do fun, arcadey-style things connect to a dedicated server. For things that are "single player", (e.g. Tutorials/Practice), I agree with you that it's to be expected that some sort of mock-loopback is likely stood up. But what was unusual in this situation is the _entirety_ of the code is there, to the point it even would bind to a UDP port and handle full bi-directional UDP communication. I would expect that for something like this, they'd include a trimmed down version, and not ship the _entire_ thing.