Without steam it defaults to doing a combination of keyboard and mouse inputs, meant to let people use a desktop. Idea is you could boot up computer, and then be able to navigate the computer to launch steam/etc.

You do have options for playing games from outside of steam:

• add games as a non-steam game to steam, allows managing inputs/etc.
• any games that use SDL will have native steam controller support (many emulators etc)
• software like Steamless controller (windows) or SISR (windows or linux) allow you to use the controller outside of steam, allowing different levels of input customization.

edit: removed sc-controller because it's apparently not updated for the new steam controller yet