RE: Is it saying that Vulkan is now supported in every game?
No.
RE: Will it work with my RX 470?
If a game has a Vulkan option such as Doom, Strange Brigade, etc, and your card meeds the game requirements then it should run. There are still a very small number of games with Vulkan Support: Vulkan (API) - Wikipedia
RE: Is it better than Direct X 11/12?
Vulkan implementations can run on Linux and other platforms. They should be more efficient than DX11 (more FPS) and generally on par or better than DX12.
RE: Can I switch back to Direct X if I wanted to?
Generally a game will have the option to run Vulkan or DX11/12 or OpenGL.