Support the vast majority of titles with minimal friction right out of the box.

Games run via Steam Linux Runtime which is the same across all Linux installations of Steam.

I don’t want to have do dick around and tweak shit when I want to relax with a video game

If you need to “tweak shit”, you have not fully compatible hardware (NVidia or so), something SteamOS won’t solve because it’s just a regular Linux distribution.

I want to be able to slap an OS on a PC and have it be Steam Deck But Bigger.

You already can. The SteamOS recovery image is explicitly for other systems as well since quite some time. People use it on the Framework Desktop, for example, even though the devices list does not feature that PC.

Don’t expect ever formal support for any hardware where Valve cannot control the drivers. They’ve been fucked by proprietary platform holders in the past, they don’t want to repeat this again. So either your hardware is fully supported by upstream kernel/Mesa drivers (which SteamOS already ships because it’s just another Linux distribution with absolutely not magic dust) or SteamOS will likely never work on those.