Wait, your complaint is that there isn't a difficulty level that challenges you specifically without being too difficult? That's... a really specific difficulty you're asking for.
Pretty much all players say this. It's kind of funny, but it makes sense - we want to feel like we're being challenged and overcoming things, without really being challenged at all. It's the reason so many games out today are so patently easy and so simple to master, and why gameplay is generally getting simpler and simpler - why make complicated mechanics and systems that require a lot of effort to win at when 95% of players won't ever fully explore those aspects of the game?
The Witcher 2 isn't a hard game, especially later on, but it does have a learning curve and requires players to prepare for fights (even if it's just taking 1-2 potions). This is, unfortunately, more than what most players, especially those into action games, are used to. So many titles allow you to run in and button-mash your way to victory. The Witcher 2 at least requires some semblance of strategy, even if it's still pretty simple once you do overcome the initial learning curve.
I guess what I'm trying to say is that I'd really prefer The Witcher not become even more of a dumbed down overly scripted action RPG + QTE fest than it already is. I mean, aside from accessibility issues, it really is one step away from Mass Effect etc.