Joystickwake reacts dynamically to game controller input, lets the system sleep if you walk away, and requires no per-game setup. It can be installed from a package (official: ubuntu, community: arch, fedora) or just copied from the source code archive and launched from a startup script.
GameMode not only keeps the screen awake, but also tunes system settings like the CPU governor for performance, and keeps those changes in place until you exit the game even if you walk away at a menu screen. Once installed and running, activating it requires prefixing each game’s launch command with gamemoderun or using a game manager that knows how to do that for you.