This was my recent experience with the third boss.
Started with a team of five level 1, 0 gene strength creatures. Artifacts were level 5 class shields with a mix of attack, speed and intelligence, so nothing really good. No perks but Hybridization and Adaptation, which don’t add damage.
Went from realm level 1 to realm level 11 killing everything, my creatures were all level 15 when I arrived at the boss room.
Twisted Devil went first, he critted one of the 3 bosses and killed it in one hit. The other 2 died to two consecutive spells. Their attacks did about 5 damage to me. Hybridization does add 50% defense, but Devils have really bad base Def and their artifacts didn’t have any Defense on them.
I think even if there had been 6 instead of 3 I would have easily won.