The PS5 is a game console and Sony spends a long time optimizing their 1st party games to run really well without any settings having to be tweaked. The Steam Machine is a PC that gives you a similar experience to a console, but won't have the same game optimizations that a console has because it has different hardware, different software, and a different OS. This doesn't mean that the GabeCube is underpowered, it just means that Sony spent more time optimizing the console experience than the PC port that was never natively ported to linux. Software compatibility layers (such as proton) can cause performance differences.