Yeah, but if you compare it with level 1 mages in BG, where you had spells like sleep, and you'd score an automatic hit against sleeping targets... I actually played a bit with a solo sorceress with the Stratagems mod and the game got very easy quickly.
Two things.
First, Sorcerer wasnt in BG1 as it was a BG2 class included along with other 3rd Ed classes.
Second, D&D had rest per day so your casting had a price, mages at low levels are pretty much one hit wonders that cannot take much abuse as you cannot spam Sleep unless you want to finish your quest when the rest of the party still havent gained a Wis bonus due to old age.
A BG2 mage didn't need anyone, since you could even melee better due to the time stopping mechanics and that ridiculous shapeshifting spell. Without mods AI in BG was not very memorable, I don't recall a single unmodded fight.
Spellcasters at higher levels are simply ridiculous overpowered, this always been the case in D&D but that is assuming they get that high level and there is also the case at lv 10+ you pretty much fighting mystical beasts and enemies, Classes always had their own power curve, Fighters shine at low level and peak at lv 10 and this is why each class had their own XP tables back in 2nd since they knew otherwise things would get out of whack.
You are talking about mods when you already appear to be using the Enhanced Editors that added a lot of shit apparently.