They might've pushed it from beta to stable reactively, but an improvement to startup times was in their beta channel last month: https://store.steampowered.com/news/group/4397053?emclan=103...

They released it like a day or two after Epic right? That is quite a coincidence ...

Good to know. I would have hated if Valve was capable of such optimization in 24h all this time but didn't if it wasn't to answer Epic.