Valve has released a series of interesting pieces of information in its Steam Year in Review 2021, including controller usage statistics. According to Valve, there are currently 48 million "Steam user-registered" controllers that are used for more than 10% of all game sessions.
Back in February, the Steamworks Update added a new game controller usage statistics page where developers can see how often players use controllers in their games and a detailed breakdown of the types of controllers they use. The data includes gamepads, flying poles, racing pedals, and even dance mats. Basically, anything that plugs into a PC and can be used to play games but not a mouse and keyboard is considered a controller.
Not surprisingly, back in 2021, more than 70% of fighting and sports games were played using gamepads or fighting arcade joysticks, while for RTS games that number dropped below 1%. Only 7-8% of players use controllers in first-person shooters. Third-person action/adventure games like Eldon's Ring of Law have a nearly 50/50 ratio between controller and keyboard and mouse usage, which is surprising because the genre usually puts the controller first, and The Eldon's Keyboard and Mouse support isn't particularly good.
It seems that many PC gamers prefer to use keyboard and mouse, even in games that prioritize controllers.
Valve provides examples of how this data can be used to help developers improve controller support for their games. Let's say you notice that the PlayStation controller is less than the global average (24%); developers should probably check to see if the correct PS button prompt appears in their game instead of the Xbox icon.
Steam's year review also notes that players' game time increased by more than 21% in 2021 compared to 2020. Daily active users are approximately 69 million, with a maximum concurrency of 27.4 million. Steam also transferred more than 32.9 exabytes of data.