Neat. Please forgive my ignorance, but what is scratch?

As for your valve question can you rephrase your question another way and provide details? From skimming your website I’m unsure of where the comparison should begin (perhaps I am unaware of all the things valve offers).

Why have it do everything?

Isn’t the guy behind systemd a (former?) Microsoft employee? I feel as though that might offer a clue as to why the trajectory towards bloat.