This isn't your typical "I start out as a farmer and take up adventuring as a profession after the dragon ate my flock" sort of story. All of the pre-rolled characters have a decent backstory that seems to indicate that they've been doing this a while. You can't tell me that in the 200 years since Astarion was turned into a vampire that he didn't pick up more than the basics of picking locks. Even worse is the thought that Gale was wandering the planes but still can't cast more than a couple of level 1 spells.
Maybe start out at level 5 or something like that. Makes it a bit more plausible unless later on all the characters say that the tadpole must have chewed on the part of the brain that contains all their previous experience.
I'm enjoying the various backstories the characters have and their different personalities, it's just this part of the equation is leaving me scratch my head.
I have to make Will, Shadowheart, Laez'el, spill the beans about their past but if Gale is an example of what happened they all didi something that brought them back to level 1. The archmage messed up with Mystra ending up killing her and with the need of powerful artifacts to avoid him to explode and erase half of the map with him and unable to use magic as he was used to.
Furthermore the really big and epic enemies can not be killed (like the demon lord in the flying squid), and the mobs in the area are at max level 4.
For our character, well the mindflyers kidnapped pratically any sentient living being they could (ehy, they implated a tadpole in a Gnoll!), so they toke a mr/mrs/miss nobody without any exceptional backstory.