Arc Raiders looks the best of this niche market right now. I just can't see how Marathon will be for casual players and by restricting it so, it will be filled with sweats after week one, causing a huge tail off to play the game.
I really hope not, but I can't see how it can survive for long term. If they ploughed more PvE stuff into it then you'll see an upturn. This is why The Hunt Showdown has lasted very well - that feels like its tapered towards PvE with a fear factor element of PvP thrown in. Superb game.