On top of their games, they have Steam, which I'd argue is more complex to scale than a "social media messaging pipeline".
But a typical game in LoL is nothing like typical Snapchat usage. Games are live and constantly changing, and therefore require complex state management, synchronization between the participating clients and the server, as well as low latency game updates.
As for Valve, the ~300 employees maintain three entire AAA video games, each with their own online communities and supporting backend infrastructure. Valve also controls the largest online game marketplace in the world with around 70 million active users AFAIK. Oh, and since you brought AR up, Valve is a pioneer of room-scale VR technology, and actually has a device on sale in the real world.
Both Valve and Snapchat are software companies. Both companies hire from approximately the same talent pool. Most of the people they hire end up writing software, which consists of a frontend and a backend. In the case of Valve, the frontend is a game or the Steam store, while the backend is the infrastructure to support the game/store (servers, databases, etc.). As for Snap, the frontend is the website/apps (Android, iOS, etc.), while the backend consists of servers, databases, etc., just like Valve.
Yes, the companies deliver different products, and they definitely may have many differences, but the core is the same in both cases: providing a software-based platform to users. In addition, both companies likely face the same challenges when it comes to scaling, given the similarities in their backends. That's why I think it's fair to compare the two.
