Agree, I own a lot of games in Steam but most come from bundles or were not bought a full price. I do buy full price games on GOG because I can have a backup offline.
The only difference is a huge difference though. Pay once for a game that you can access anytime versus paying continuously for the rest of your life to keep access to a game.
Some games are not worth keeping access to and subscription may end up being cheaper, but it is trading one benefit for another.
The only difference seems to be that steam doesn’t demand a monthly subscription cost, yet
Which Ubisoft isn't doing either. This is just Ubisoft's gamepass style subscription, which has been available for a few years now, it's just getting a 2 tier pricing model.
I'm not enough of a Linux user to inconvenience myself so I'm just using Steam. The cloud sync is the killer feature for me - if GOG had something like it even if I have to pay extra, I'd so use it.