Just running down your post to answer every question I can. Here goes:
Do you play dungeons on normal?
I raise the difficulty of any dungeon I run into so that the challenge is “hard”, that’s about as high as I can succeed at.
do you clear all the rooms in the dungeon?
Yes. I will also run a dungeon as much as I need to in order to get a task done, one other issue I have with this game. I’m looking at you, Bevelros.
Having the “problem” of going against 3 level higher monsters in the new map area? Best way to level up faster is kill stuff that is higher level so just go fight them and soon you’re same level.
This doesn’t help if the monster is EIGHT levels above you and a surprise. Looking at you, Ancient Treasure Fiend.
Can’t kill them? USE burst. Don’t save it. Kill enemies one by one from highest threat or lowest health depending on if there are healers and how many enemies etc.
Didn’t work. He 1-shot the entire party with HIS burst. I think he read your post.
Bad combination and/or perk choices? Maybe I had one healer (Bretto) one tank (Gully) and one DPS (Monika). What do you recommend?
Too low level gear? Best that I could craft/wear/buy from the collector at the time. Always.
If you’re lower level than monsters in dungeon only pull minimum amount of units to you at once in a dungeon until you feel comfortable killing more at once. Anways the idea that you can’t kill stuff in the game if they’re higher level is not a thing.
I try. Sometimes it just doesn’t work that way. Anyways, the idea that you can’t kill stuff in the game if they’re higher level is absolutely a thing. Looking at you, Mana Devourer.
Yes making questions here that lot of them can be obvious but i’m just guessing here what might be the problem.
You’re a poor guesser.