The boss in the story is so strong and stage only once complete, i don't like this

Stage 3 seems impossible! Am I crazy or is stage 3 nearly unbeatable? I've tried it with so many different classes and builds and only even made it to or past wave 14 two or three times. zZz It seems like too far of a step up from stage 2 having two bosses on wave 14 and two on wave 15. What armor or shield do they have. Ugh!

The boss fight was too ez