I'm not sure if it's a recent update, but now the store correctly indicates that Ruiner has Achievements, Leaderboards, Cloud Saves and Overlay.
Not sure about this either, must have been some technical hiccup. Glad everything's ok now :)
Hi, I just accidentally discovered that the Steam version of the game has two extra achievements, "Peace was never an option" and "Seasoned fighter", which you added on Steam along with the Arena.
Could you add them here on GOG too?
Edit: The missing achievements were added some time ago.