Please no level scaling.
I still remember Oblivion: After fighting thouthands of demons you have epic battles against rats and goblins. In this game you have the feeling you get weaker as you level up.
Maybe exp scaling works. That means you get little or no exp for fighting weak enemies and many exp for fighting hard enemies, depending on your level vs the enemy level.
Larian did this in DD and D2 (maybe others, I am not sure). You could exploit the system by killing everything first and returning quests later because quests gave always the same amount of exp.
One of the few games with just the right difficulty was "Legend of Heroes. Trails in the sky". Monsters gave lots of expn when they have a higher level than you and they give only 1 exp if their level is much lower than yours. Quests do not give exp, only combat. But this is a very linear JRPG (a very good one), and the system makes sure that you have always more or less the same level when you meet the next boss. I am not sure if such a strong exp scaling works in a more open world.
Prof. Dr. Dr. Mad S. Tist
World leading expert of artificial stupidity.
Because there are too many people who work on artificial intelligence already
