I'm not the only one. I met someone in discord, who dunnit, too. Without tricks like me q: .
The last boss was awfully easy with fire, poison and fire resistance on 90 %. The bosses are easy with the moment, when you are able to juice resistances.
Atm I'm adding the Damage, the boss deals into the wiki - for example
https://crashlands.gamepedia.com/Baconweed_Fairy or
https://crashlands.gamepedia.com/Ynnix in the small boxes at the side. I also added the signals name.

The hardest part of hardcore in my opinion is just, that every enemy with a higher level is able to one-shot you if you don't got resistances. So you ALWAYS need to be extremely carefull and sure there's no dangerous enemy near you.
And yes, You will face 9 bosses and hewgo just at the end.