You in chapter 2 are send on valley of mines to SCOUT!!! Not to try to be the hero and kill all orks. If you try that, you will gonna die. Even if you have the Beliar's Claw as a warrior, you have no chance. Your mage, able to cast only circle 2 spells too. Not much chance against then.
I don't quite understand the relevance of this example. It's intentional - and a great use of Leveling system. Nothing you mention here refers to balance. It would be, if for example, you were send to clear the area, and you could easily do it with mage, but not with warrior.
It's not uneven balance - it's game gating content and storytelling though use of high level enemies. That's good. Poor balance is bad.
We don't need to be able to beat every encounter in every moment of the game, with just perfect difficulty, with the exactly same resistance no matter what party we use. Poor balance is if certain encounters are unintentionally easy or difficult. Or if certain classes are simple overpowered or underpowered throughout the majority of the game. It is fine for them to both shine and underperform in various situations. That's balance as well.