So it sounds like class restrictions are more prevalent than Drakensang, but less prevalent than NWN/2. Yet, NWN/2 allow multi-classing…
you can't "multiclass" in DA basically because there are only 3 classes. Now, within each class you can select up to 2 specializations, and within each class, you can focus on several different styles, or be a jack of all trades (within the class). Like, a mage has several schools (a mage could be a shapeshifter healer/fire blaster, another mage can be a spirit healer psionicist/water blaster and another could be a bloodmage necro/earth blaster. A warrior could be a templar sword and shield fighter, another could be a revenant two handed/archer, another could be a do it all two handed/archer/sword and shield/dual wielder, although he wouldn't reach max on anything I think)