There is only 1 Steam client for Linux, and there will only ever be one client, and that client has had basic issues (context menus being a completely new window that steals focus, comes to mind instantly) that have been unresolved year after year.

For GOG, there are plenty of clients for Linux [1][2][3][4], And they are open source, I can go and talk to the people making these clients directly, I can give feedback, I can make changes to make these clients better (and to a small degree, I already have).

[1]: https://sharkwouter.github.io/minigalaxy/

[2]: https://sites.google.com/site/gogdownloader/

[3]: https://heroicgameslauncher.com/

[4]: https://www.hyperplay.xyz/

This is true, but there are pros and cons.

Pro 1: reduced lockin

Pro 2: open source options

Con 1: not all options are all that easy to use or feature complete, making the "choice" a mandatory QA/research task, rather than a way to exercise personal taste/freedom

Con 2: no galaxy-only features like achievements and save file cloud sync

(My personal testing led to choosing Heroic)