Do you have to work up your skills in order to beat bosses?

I die a lot. From forgetting to eat, to falling off beams while building, or getting smacked in combat. A buddy and I went to fight Moder with top level gear up to that point (Wolf/Cultist armor, Drauger Fang lvl3) but our bow skill level is around 15. We fought that sucker for over an hour and barely got her below half health. We tried smacking her with silver swords and axes as well but barely chipped away. I believe my melee skill is mid 20’s-30.

What level are you aiming your attack skills to be at when you hit the mountains/plains??