Ok, so in BG:EE, Sorcerers got a kit.
And it was cool. Dragon Disciple trades one casting of your level 1/2/3/4 spells per day in return for -2AC, 50% Fire Resistance, +1 con (which isn't really a big deal on mages), better hit dice, and the breath. Basically, a slightly less capable Sorcerer that compensates with slightly better natural defenses and a nifty ability. All in all, this is a fairly even trade in BG:EE, maybe even slightly in the favor of the Kit over the vanilla Sorcerer.
But with BG2:EE on the horizon, a lot of things change. In mid-late SoA and especially in ToB, AC becomes less and less important defensively - enemies with very low, even negative THAC0 and decent APR start to become common. The extra HP from those early levels might save you - from about one additional attack when enemies regularly hit for 20+ damage. And now you're not giving up just low-level spell slots, you're giving up an extra Time Stop or Improved Alacrity, Horrid Wilting or Power Word: Blind, etc.
In short - what is the Dragon Disciple going to get to compensate for the loss of those oh-so-incredible high-level spell slots? I hope it's something beyond further Fire Resistance/AC/Breath Weapon progression!