Fortnite Battle Royal, the free, 100-player PvP mode available on PC, PlayStation 4, Xbox One & Mac has surpassed the all time top concurrent players of PlayerUnknown's Battlegrounds (PUBG.)
What I think happened with PUBG and Fortnite is; PUBG stoked the fire for battle royal gaming and sold a tonne of copies. Fortnite rode that wave create by PUBG by releasing a free-to-play game mode and change the gameplay just enough to create a more varied and enjoyable experience.