Is Steam or Galaxy 2.0 more system intensive while playing games?

Steam uses more outside the game but when its running they both sit in the background pretty well until you find Galaxy downloading bullshit updates during play
example Galaxy can be set not to download 'galaxy' games during play but it will still download Galaxy updates and playing 3rd party games linked to Galaxy doesn't stop downloads so overall Steam is a much better system

Unless you're affected by the known memory leak issue they've been aware of since the "new library" update was in beta and never fixed. But even that has been mitigated sufficiently that it rarely causes issues unless you're keeping your PC running for a month straight without a restart. That said, in some cases it can cause a complete system freeze that forces you to restart your PC to get it working again, so that's fun. And yes, that's the same update that's been known for almost as long to be a literal health risk for some users, among other problems.

The question is also: does it matter in reality?
I don't want to dismiss your point, but just to use myself as an example, both Steam and Galaxy are negligable during play, but Discord uses 2% cpu on my system just sitting in the system tray. Playing flac music can be 3-5% and having a youtube video on in the background is 3-4% cpu for 720p or less, 8% for 1080p and 20%+ for 4K.
So it is worth it to actually look at what uses resources in reality, and not focus on a client.

Galaxy does log A F**KTON of useless stuff. It is on a nvme drive so it doesn't slow down my system, but it does annoy me. There is no reason for 300+ MB of log files.

I was looking for the actual system requirements or system usage stats.