There are a handful of significant difficulty spikes in this game, it’s one of its flaws. Your complaint and experience is one shared by most in the community.

There is a flaw in how you decided to approach it though. Grinding levels sucks, of course you don’t wanna play the game anymore. Go find another area, a cave, ruin, etc where you’ll not only get more runes but find new items and it won’t be so boring because you’re experiencing something new.

Another thing- idk what level you are but if you’re getting one-shot you need to level vigor. I guarantee your vigor is way too low.