You're missing the point which is the over the top epic stories rather than if +/- a few levels makes more sense or not.
Yeah Jaheira and Khalid should maybe be level 4-5 to reflect their backgrounds more accurately, but they still don't have a completely bonkers backstory that claims they are/were epic heroes before "tadpole".
And yet I'd take the extraordinary companions from Planescape over BG1 companions any time. Whether someone writes "ex farmer" in their biography doesn't make a fictional character more interesting for me. And it wouldn't surprise me if Astarion managed to gather more fans among BG3 players than Khalid ever did.
edit: I also don't see how Astarion is claiming to be an epic hero (or villain). He was under the rule of his master for two hundred years, and as such not allowed to act true to his monstrous nature; before that he was a city clerk. So where would he get that epic experience? As for vampires being rare, for that to be believable you'd have to retcon BG2. Because while In BG1 it was skeletons and ghouls, in BG2 the city is overrun by vampires. You bump iunto them in the streets quite often (nevermind the liches hiding in dungeons). Wyll I don't find any more epic than the warlock class in itself., considering you create a character by making a deal with a powerful magical being. Laezel is a standard fighter, and not even considered an adult by her people (according to her). Gale & Shadowheart are the ones I am not sure about, because I suspect one is lying and the other doesn't know the truth.
