He's right, Corwin is talking about NWN Sorcerers, not BG2 ones. In BG2 it's all about what party you bring along - when it comes to individual characters it's just important to keep their main stats high (charisma for sorcerers).
As for parties, I prefer 5 people instead of the usual 6, since you level up a bit faster then (you get the same amount of xp, you just divide it on X number of characters). My usual setup consists of: 1-2 capable of healing, 1 excellent caster (pure, not hybrid), 2 close combat folks. One of them must have find/disarm traps (as in, have at least some levels into rogue).
For a good aligned sorcerer my party usually looks something like this:
Main char (sorc)
Keldorn (excellent fighter with Carsomyr + Bracers of Dexterity)
Anomen (best healer, since he, for some reason, starts at normal priest level, but has warrior levels as well. Basically, he's got the warrior levels for free)
Imoen or Jan (for rogue stuff)
Valygar/Minsc (I actually prefer Valygar since I can give him the Celestial Fury, one of the strongest weapons in the game pre-add-on).
If you want romances, you have to squeeze in Jaheira or Aerie.
I've played through the game a bunch of times with this party. Don't even know why it's still fun, considering there is no difference in the various games.
Edit: Keldorn is probably my favourite NPC. Some people don't like him, they find his dexterity too low, but I know how to get a pair of gloves giving him 18 dex rather fast. The reason he's so good is because he's a caster-killer, and casters is the biggest problem you'll come across. With Carsomyr he gains 50% magic resistance and the ability to dispel with each hit, and his dispel spell (because of his subclass) is incredibly powerful - it has a much greater chance of dispelling than other, similar spells. One of Keldorns dispells is usually enough to remove every buff from all enemy casters. Also, he's got True Sight, which enables him to remove those annoying see-through-buffs that enemies tend to pop on (with that on, for example as an effect of Greater Invisibility, you can't use direct spells on them).
If this is your first playthrough, I strongly recommend bringing him along and giving him the right gear to kill casters - it will save you a whole lot of trouble. Well, unless you play evil, of course.. in that case he'll leave you, hehe.