I talked about the

substantial enough to need an installer

line. Like what makes a game substantial enough to need an installer ? Steam and every other game launcher with install capabilities is more or less just a fancy installer. There is no more effort needed for a publisher to generate a new installer binary than it is to generate a new steam patch. Even if gog installers are offline it’s more or less an archive with a binary stub to unpack it and the install script. This one is on the publisher and not on gog. And for the version difference, do you have an example where the gog and steam versions differ ?

I don’t get that installer thing ? Steam downloads the game executable as well as all of the required libraries and assets into the steamapps directory and runs install scripts. It also runs potentially needed dependency installers like c++ visual studio redistributables or directx installers. The same thing does the gog installer. And the games I own on gog have always had version parity with the steam versions. I thought this would be the standard if a publisher publishes on both stores.

So what’s the problem about using third party clients like heroic game launcher ? Or did I understand the first line of your post wrong ?