Promising perfect work between different launchers was always going to be a shitshow because of two simple things:
-You do not have a partnership and you need to rely on public APIs. Using public APIs means that the interaction will always be a pain in the ass and buggy as fuck because your code is working on loopholes the APIs leave and not using them as intended, so a desync for whatever reason will fuck things up (or a slight change of how the API works but not its end results can fuck you up too).
-You have a partnership and can have more in dept h comunication with the publisher. Now here you rely on the partnership being in good faith and actively partnering with you when they make major changes to their service (and take you into account). Which in most cases they will kidna forget, so your partnership application will slightly get worse.
Now, once you combine that with the rest of the GOG (which you fully control) you end up having a mess of different levels of interactions that do not give a cohesive feeling, which was the full idea of Galaxy 2.0.
You are correct for some of the features, like the linked social stuff, syncing achievements and stuff. It is complicated and Rome wasn’t built in a day.
The thing is, some of GOG Galaxy’s 2.0 features (such as one launcher for all) have been implemented in other software. They really have no excuse for their poor launcher integration other than their software being poorly designed, and them not fixing it.
I know I go on about Playnite, but it’s predominantly developed by one person (with lots of extra features being made by the community), and its ability to hook into pretty much every PC launcher except EA Desktop (which, apparently, will come once it is out of beta) is outstanding. It pulls metadata from each store, or IGDB, or SteamGridDB, has advanced library management and sorting options and launches all your PC games from either a desktop or 10ft UI.
When add-ons are considered, you can also add games from GeForce Now and Game Pass cloud, pull achievements from anyone who offers them using the SuccessStory add-on, get instant access to how long the game is with the HowLongToBeat add-on, and lots more.
The problem with GOG Galaxy 2.0 is as much poor implementation of sound ideas as it is difficult problems to solve. GOG basically released the client in its current broken form and have not meaningfully changed how it worked. Meanwhile, open source software funded predominantly by Patreon has leapt ahead of it and does more improvements in a year than Galaxy 2.0 has done in its entire existence.
I want GOG to succeed because Steam shouldn’t be the only player in town and what GOG is doing is offering differentiation that is beneficial to gamers. But their client sucks ass and they’ve shown little interest in fixing it.