PUBG is scared of anyone fucking with their genre because quite frankly they've made a game that....well it isn't very good. I mean the mode itself is good, and the game is fun enough that it is currently rivaling Counter-Strike and Dota in concurrent players, but the system in which the game is built on....just isn't very good.
Any other developer with a decent pocket book of funding behind them, can make a Battle Royal mode that would look better, play better, feel better, and just be better, if they want. Judging by the sheer success of PUBG, it should be obvious that the big publishers will be looking into doing a mode like this and that scares the shit out of PUBG.
Trying to copyright a game mode is just dumb, look at League and Dota, look at any number of FPS games. That's like trying to copyright Team Deathmatch. Are you retarded PUBG? You must be...oh wait, you are just scared because your game is shit and has built a success story by capitalizing on a really really good game mode.
Enjoy your short term moment in the spotlight PUBG, because someone is going to coming along rather quickly to do exactly what you do....only better.