I mean...you can call it what ever you want, but Sony had PS Plus giving out free games...TO DOWNLOAD for years before Gamepass, they were already deep in that ballpark to pretend such a concept wasn't already on their radar in some form.
So the idea of paying for some sub and getting games is what PS Plus is. To say to have more games is simply an extension to an already existing thing or that you buy into some vault simply isn't some far out concept beyond what PS Plus is.
They just already had a whole sub for games, download for this, stream this thing going on for years before gamepass. So I don't think either are copying each other as the model already exist else where and downloading a game and paying for a sub isn't some revolutionary idea lol