Imagine a party of 4 people.
One pure warrior
One pure ranger
One pure rogue
One pure mage
Now lets say you have to lose one of them. Which one is most expendable?
My answer would be "anyone but the mage".
Well, in order of importance.
1. Mage. Far too much is lost if you have zero spellcasters.
2. Warrior. Deals huge damage, surprisingly versatile.
3. Ranger. Bows are pretty good and you'll need at least one high-Perception character.
4. Rogue. Not necessarily horrible, but worse than the others.
Hybridization can kind of alter the situation, however. For example, I ranked Warrior where I did because having access to Man-at-Arms is a good thing, but you can make a Rogue-ish Str/Dex hybrid with those and use daggers instead of a two-hander, and that could work.
Generally, though, I think the best thing is to ditch Rogue, then for your fourth character hybridize the first two. This gives you some resilience if either of your two most important characters -- the mage or the warrior -- fall.
I mean, I haven't been trying to say that spellcasters are horrible. Far from it. It just seems might weird to me for you to be constantly going on about how the second most powerful character type in the game seems underpowered to you. If I did a double Lone Wolf playthrough, it would be a mage and a (Perceptive) warrior; I actually can't imagine going through the game without one.
