Well I can say that this map has some heavy handed difficulty curve for sure that skyrockets into oblivion after second Alef overload ends.
But all is not lost. Me and my buddy were farming this mission for a LOOONG time - and we are getting pretty good at it either with antagonist or not, trick is in having characters that on your team that know what they do:
Hans with "WARM" gun - perfect for firsth phase, good for clearing and avoiding beherit spawns and does well vs blobs.
Konstantine with either OGON STORM or Hornet - simmilar affair but you trade burst DPS for sustained DPS choosing different guns with him. Good overall at every stage and at dealing with beherit spawns, really bad at running.
Ginebra with her unlockable guns - if you can aim well she can pretty much oneshot blobs and beherits and can run from them for days. Do not use her basic gun there - its useless and people will hate you for a good reason.
Mikah with unlockable guns - you can "climb holo-glitch" to make unkillable bait for beherits, you do ok at every stage, the only problem is that you must conserve ammo big time.
Suboptimal but still fine:
Shae WITH FOCUS KAA7 ONLY - then you do fine more or less. DO NOT bring Shae with any other gun - you will have good time at stage 1 shooting squids, but in stage 2 you will be useless at doing anything.
Harek with base gun - you will do fine, but if Beherit will ever hit you with his AoE you can instantly bite the dust - oneshoting blobs are fun thou.
Avoid:
Kuzman - takes ages to kill anything, especially blobs. Can once in while kill a tons of beherit spawns with well placed skill - but better not get into such stage of spawnage.
Alicia - just no. You can run fast, you can avoid stuff, but you cant clear spawns for good and must stay nearby blobs (and thats not an option vs some of them)
Dion - same as alicia, made worse by the fact that your shield is useless in second stage. You can kinda do it with "It Happens", but I still think you better be using someone else.