Your argument is interesting. I get that it's upsetting that Mac isn't well supported.

Valve isn't obligated to continue supporting all its games and software features on Mac, especially when Apple's reluctance to natively support Vulkan and other cross-platform technologies makes game development more complex. There's no excuse for Steam on Mac...

You wrote the excuse/reasoning for Steam not to support Mac before saying there's no excuse. If Apple enforces their control over their software and hardware by making everyone developing sign restrictive EULAs and dictating what technologies can run on their hardware, why does Valve have to play ball with that? Apple has had no interest in courting gamers to their platform for several years, so it is their problem why Steam has become unsupported. It seems like they even tried by converting their app to 64-bit just for Apple, then they get shut out because the architecture changes to Apple Silicon. How many hoops is Valve expected to jump through?

Epic is the company trying to be the Amazon, Walmart, etc. of the gaming industry by "disrupting" the existing ecosystem with free games every week, paying devs off for exclusivity with their fortnite cash. It's clear as day when they take over is when they are sure to enshittify themselves.

GOG games I do support, but I'm just sad that they haven't done much for Linux.

You didn't mention itch.io, which has a well-functioning app (at least on Linux), and a revenue sharing model set by the developer, and a pay what you want scheme for buyers.