MaximumBunny: Galaxy suffers from drawbacks. It has to be an extension of the GOG website for people who want to opt out of it, meaning any features need to be dually-available without it. Which makes it difficult for them because there are more things that you can do with software than with website functionality.
So tldr: it'll be added to the website and Galaxy simultaneously, and one isn't going to possess features over the other. It's simply going to attempt to make them more conveniently accessible.
In particular for the features that the OP asked for (seeing friends and their libraries, wishlist) - this is probably something one could easily implement in both since displaying lists is something that browsers and desktop programms are both quite capable of.
From a software design point of view: One could have an internal engine providing the services (get list of friends, ...) and then both, the website as well as Galaxy, are connecting to this service and display similar information in a slightly different way. And if Galaxy has the edge for some social features that cannot be conveniently be displayed in a browser (like video chats maybe) - just make them Galaxy only. As long as I can download the installers and get meaningful notifications of updates also through the website, everything would be fine for me.
Hammercorps: So, in GOG galaxy, are there profile options where you can see your friends libraries, wishlists, etc. like in Steam?
No particular reason, just curious.
Unfortunately it's still not very good in that regard. It's still beta and the progress is kind of slow lately. Judging from the speed GOG showed lately it may well take another year before these things work reliably.
Basically searching for members is pain in the ass. Wishlists are okay, you can decide for yourself in the options (website or Galaxy I don't remember) if you want to share the wishlist with everyone, friends only, noone (and hopefully this is the default) and library sharing is not possible afaik unless you use a dedicated third party service like
barefoots essentials and then share library to gogwiki (or so).