I cant help the feeling you are overthinking that level stuff too much ...
Also where did you get that idea that our companions were superpowerfull?
Wyll is a fraud and liar ... i wouldnt be surprised if he would reveal later in game that all his heroic deeds was just fabricated stories ... simmilar to movie Dragon Heart ... Mizora showed as some fierce monster, Wyll "slain her", and then money fame and fortune just come naturaly.
Or it was whole her trick and he didnt know.
Lae'zel is still a child in eyes of her people basicaly meaning she only completed basic training.
Shadowheart have Format:C done on her ... by pure fantasy covenience she still remember to talk.
Astarion is old as fuck ... but what did he do so far? As far as we know all his Vapire work was: show up on party, wait until some noble gets interested in him, and then lead them back to his master.
I bet he would have level 20 in etiquette, and knowledge of vines by that time ... but as an adveturer? You hardly can find anyone greener than spoiled noble, no matter how old.
And finaly Gale, the only character who indeed maybe had some real power in the past. Even if we put aside that he contain artefact that quite litteraly "syphons magic away" ...
All his stories and boasting about his power and talent are in the past ... i mean he certainly made it sound as if he were level 20 just 20 minutes ago ... but when you listen to it very closely, you find out that everything he say can perfectly fit to a young man, maybe even kid, that us just few lections ahead compared to other kids in class.
I would say there is serious possibility that he was never as superpowerfull as he let us believe.
