My biggest problem with GOG is that Galaxy doesn't rival Steam, same as every other launcher. For example, GOG hosts a lot of older games, that used to be their bread and butter and even their namesake. These games generally don't have native controller support, so if I want that, I have to launch them through Steam anyway to use Steam Input. If I want to play something on a Linux device, which is now more likely than ever since I own a Steam Deck, the fact is that it's a pain in the ass to deal with GOG even with their minimal DRM stance (because they allow DRM now seemingly so long as it doesn't prevent the player from beating the game) because of the lack of support, making it more reasonable to buy games on Steam, even when it's a game that does support controllers (like how I own The Evil Within on GOG).
The big feature of GOG Galaxy is that you can pull every other launcher into it, but that doesn't matter to me when I still have to launch everything via Steam anyway. Feels like they're missing the point a little bit.