Yeah, cheesing Atheon until they fix it today is a lot easier solo, especially in hard mode. You can even do it at 27 although you will die a lot as you get 1 shot by the bolts. He just moves a lot more steady and predictable when you are solo, even when other players are dead he tends to jerk around a lot and pause which screws up the timing.
Makes me always laugh seeing people post here and elsewhere demanding locks (only) with experience to kill atheon for them. screw you random stranger, its easy enough to get a checkpoint so why would anyone bother doing you a huge favor that is much harder than doing it solo.