Just barely managed to beat it on my third try. Solo, because I wanted to prove a point to myself I guess. Mind you I'm not a power gamer; I play this game very casually and don't care much for minmaxing and whatnot, so my resources are somewhat limited. Safe to say, this was the hardest and most nerve-wracking thing I've done in this game. I did it with Protea and an Incarnon Lex Prime. Maybe not the best choice but it worked? In hindsight I really should have brought some knockdown immunity because being 2 hits away from death at all times was not good for my heart with the amount of staggers and knockdowns in this fight.
I think the ability nullifying attacks are a good idea for tackling difficulty. The overwhelming damage, less so. Not to yell "nerf!" but I think that the amount of health is too much for a boss that's locked behind a good 10-15(?) minutes of mission objectives for every attempt. Maybe introduce some sort of checkpoint to let you use your revives but resetting the boss fight to where you have to summon it again? Also, I think phase 1 should have at least a few basic(non-eximus) mooks spawning so you have some source of health/ammo and targets for abilities to function.
Wow, my first forum post since... 2016?!
Or, depending on the arena, just outspace it. The beams only seem to reach ~10 meters or so. But bullet jump + aim glide is definitely the way to go.