Some have started that the explanation for them being Level 1 characters is that their 'powers' were removed by the tadpole, which to my mind is an awfully trite plot line.
This is a little different story ...
But what is even wrong about them being Level 1?
< Shadowheart >
Kinda easy ... memory wipe, what else is there to say.

< Astarion >
This one seem completely fine to me. Yes, i get that he is cencuries old, and probably should have some experiences ... but on the other hand, if you talk to him, all his previous life was just about "being noble" ... so, it makes sence that he have no experience as Rogue, he never needed to picklock, stealth or shoot/stab anything ... he litteraly tells you that his work was to charm some noble lady and bring her to his master's lair. :P
< Wyll >
This one is tricky ... he is kinda folkhero, i dont even know what "great acomplishments" give him his title ... he introduce himself as "slayer of kobolds", and you met him a little later than everyone else, so he is not exactly "level 1" ... maybe his story isnt so epic as he claims.

< Gale >
Yes, i get that ... Gale claims that he was miracle, there is a lot of stories of his spellcasting ... but then he kinda screwed and he have now something in his chest that consumes magic. To me, its quite good story (not best, certainly not exceptional, but accaptable) that his talent was damaged by this. :P
< Lae'zel >
She is actualy the only one who seem odd ... Githyanki should have precise training, and herself mentions countless times that she do have precise training ... yet, it dont seem like that. :-/ But, for this one we can easily use the tadpole excuse. :P
(minus Lae'zel, whose only exception is that a Githyanki be a rare sight in Faerun?)
And that is what i dont understand ...
Everyone in Faerun knows that Githyanki exists ... they just dont appear often, but it is possible.
Everyone in Faerun knows that Vampires exists ... they just dont appear often, but it is possible. What is so odd about Astarion except being a Vampire Spawn?
Everyone in Faerun knows that Hells exists ... beings that live there, just dont appear often, but it is possible. What is so odd about Karlach except being Hells General?
For Lae'zel is that okey ... and for everyone else its seen like superspecial überCool background.

I wonder why?