I don't really see it any different than stealing the concept of FPS from companies that came before, or from stealing the concept of video games from the original creators. I see no issue with it, much like I see no issue with all sorts of games borrowing from LOTR (or from other sources that eventually trace their way back to LOTR). Even PUBG stole the concept from others. It reminds me a lot of Hunger Games actual battles (not the teenage romance angst portions), and Hunger Games effectively stole the idea from elsewhere. (And likely I'm missing links in the chain of who stole what from who, and I don't even like the idea of calling it stealing.)