i think you understand something wrong here.
The steam-runtime is active by default in
when you also install steam-native, it will be disabled and the system runtime will be used. (thats what "native"-runtime means. This will be triggered at runtime
However, even when
steam-native is installed, you can set
STEAM_RUNTIME yourself and that will be used.
Usually all games should run nur with steam AND native runtime. There is a known issue now with optirun/primusrun (call it whatever you want) and mesas dri prime. Because of a change in how steam handles graphicsdrivers its (for many) not possible anymore to just call steam on the dedicated graphicscard. Thats why everyone should let only the game itself start with the stronger graphicscard.
I will not blame anyone here, but with both changes (our new client AND how steam itself acts now) you should not use any strange "hack" anymore. Like @BS86 said here, they cause some trouble you will not have on a "fresh" manjaro installation.
If a game still not runs please start steam on the terminal, start the game then and post your output here. We'll try to fix it.