Amount of xp doesnt play that big of a role anyway.
This game is specifically made to provide players with many different skills and spells - that are specifically made to synargize and combine with each other.
The players skill and imagination on how to use and combine all those features is much more important in combat then just xp or levels themselves.
And no, there is no possibility to outlevel stuff, because the devs know the exact amounts of xp in any area. And therefore can adjust the hardness as they want.
XP plays a huge role in this game. It is the sole driver of your character's progression. Without it, there are no level gains, and thus no new stat points, abilities, etc. Levels gained via XP also affect which weapons you can use, and thus the amount of damage you can do. If you gain zero levels, you'll be hard pressed to make it outside the western forest. If you can't do that, there isn't much game to play.
In addition, it certainly is possible to outlevel "stuff." In my first playthrough I was very much overleveled for the orcs on the beach area. I believe I was level 8 before I tackled that area. As such, it was a walk in the park.
Your comment about the devs knowing the exact amount of XP in any area is true. But the developers have no control as to how much or little of it a player decides to acquire. Nor do they have total control as to how a player progresses through the game.
I think Gyson's main concern has to do with a player that does every single side quest. Will that character be such a high level before moving to the next area that the initial encounters will be trivial? It is a legitimate concern, though one I'm not sure the developers can do much to resolve.
I don't think end game will be much of an issue as there will be a level cap. That means the final encounter can be tailored for a party that is level 20 or whatever the cap may be. But the battles in between could play out much differently depending on how a player goes through the game.
