that’s fine and all but the problem with the debian based SteamOS were the horribly outdated GPU drivers.

SteamOS doesn’t use plain upstream GPU drivers. Back when SteamOS 3 was announced, Valve employees said in interviews that switching to an Arch base would allow them to more frequently update the OS, yes, but now with SteamOS 3 being out since quite some time it became clear that this is simply not the case. Big Arch package syncs are a rare occurrence, kernel and Mesa are maintained in their own downstream branches.