Bug or unfair mechanic with Simulacrum-kosis and CWS-unearth skill

I am aware that it is impossible for CWS+RF skill (CWS 1.0)) to defeat kosis in simulacrum. I have specifically spent time, effort and currency therefore, to spec into CWS with unearth skill by player emiracle (details here: https://www.youtube.com/watch?v=l12OxqCLcE4) with the CSW + Unearth + Detonate Dead (CWS 2.0) where it is clearly shown the player can defeat kosis with this skillset.
I am providing my in-game configuration in this pobb link for your reference. This is my actual IGN: "Grond_Daddy" - https://pobb.in/ZqDHtEV29X4R

My observations after playing this skill with multiple simulacrams are as follows:
Mechanic:
M1. Kosis and omniphobia (aka bosses) spawn during gameplay, as part of 15 waves. At what point in the wave they can spawn is non-deterministic (beginning, middle or end is random).
M2. Omniphobia has a constant attack with no cooldown, but he has no invulnerable phase and he has no regeneration either
M3. Kosis has many attack phases and he has a invulnerable phase during which he also regens.
M4. Kosis has many attacks, relevant to this discussion is the slam and shockwave he does after the regen phase.

Play condition

P1. During a wave, the bosses spawn together, closer to the middle of length of the wave. In this phase a CWS 2.0 player can comfortably dispatch both of them as he uses the consistent mob spawns during this time to ignite proliferate and transmit the explosion to the bosses.
P2. Bosses spawn towards end of the wave, and due to the sufficient availability of mobs, it is possible to somehow dispatch kosis first (who didn't spawn very tanky) and with omniphobia remaining with no more mobs. During this phase, because omniphobia doesn't have a regen, the player slowly but consistently provides sufficient single target damage to dispatch omniphobia in the end (takes under 1 min)
P3. Same conditions as above, the explosion generated by omniphobia's ignite creates enough DoT for kosis to take damage until he dies.
P4. This is the problematic scenario. Let me break this down into a separate section below

Problematic gameplay phase
Nearing end of wave, omniphobia is somehow dispatched and kosis remains, along with some 50 monsters in area.Please note, almost 90% of damage taken by my character is recouped as life through various jewels, gems and accessories. I am also giving out around 2.5 mil damage (see pob for details).
Now this is what happens:

PG1. Kosis has a timed regene+invul phase which he insta activates as the monsters are made to seek to him by players. While the monsters are killed by unearth+DD mechanic, kosis' being in invulnerability causes no damage to him. Monsters died for nothing. This mechanic was observed to be repeated faster than normal for some reason, and as player repeatedly tries to lead the remaining packs to detonate closer to kosis. Now, kosis is left with more than half life health and no more mobs in area.
PG2. Kosis and player are going mano a mano at this point. Like with omniphobia, player is slowly causing damage and kosis healthbar is constantly ticking down.
PG3: Kosis goes into invul phase at short invervals and repeatedly. During this phase, not only does he not take any damage, he is also regenerating both health and ES rapidly.
PG3: A charged kosis immediately goes on slam and shockwave attack phase on the player. This is easily tanked by player and continues to attack kosis.
PG4: Steps 3 and 4 repeat in regular time intervals and player progress of damaging kosis is being reset. Player has no more recourse to extra monsters in game and lacks any tactical advantage over kosis. kosis however is constantly recuperating his health back and launches heavy physical damage shock and slam attacks over player that seem to get stronger after every regen phase
PG5: Player and kosis are now locked in a dance to death that has devolved into an endless loop. Player does enough damage to bring kosis health down but kosis has the ability to regen near constantly and is invulnerable in that phase. Player however has no means to use any game mechanic at his disposal to cause damage to kosis as no more new mobs spawn.
PG6: The only way to end this impasse is for player to stop attacking kosis completely, while kosis continues his regen and slam + shock phase attacks towards player. Since kosis is steadily buffing these slam and shock attacks, he eventually musters enough damage to kill the player who loses XP unfairly.

Suggestions for making it less unfair to player:
1. kosis stops his invul + regen phase once there are less than 10 monsters in area
2. kosis mimes omniphobia's behaviour once there are less than 10 monsters in area
3. kosis can regen but the regen phase takes longer and longer to activate rather than regular intervals like in the present. This makes the fight still hard but gives the player a fighting chance to break the cycle of making no progress as it stands now.
4. I leave it to devs to propose another suggestion to make it fairer to the player

The status quo right now is stacked heavily against the new CWS mechanic, which clearly has the ability to kill kosis solo. This is unfair to player and penalises them for no reason. It is demoralising to play the game in its present form. I request the devs to roll out a patch to let players enjoy this newly discovered mechanic/interaction to win over a very difficult and rewarding in-game boss.

Thanks in advance.