I honestly think that all something like Reflex needed to have is a genuine single player / coop aspect that flows almost exactly like Quake 1. Fighting massive numbers of enemies and leveling up ect.
I feel like what we are really missing is solid single player / Coop experience with these styles of games. That would attract the big audience. Quake champions would be butter if it had Doom 2016 style SP / Coop tacked on.