... or Wyll not being a Warlock. But that's the 3 whose class is strongly tied to their story.
But Astarion could be ... well, Rogue works, but perhaps also Bard, or Fighter ... Whatever, he's a noble from the city whose profile does not scream "adventurer".
In my view, Lae'zel could be Fighter, Barbarian or Paladin (of Vlakith) pretty much equally.
Likewise, Minsc isn't the most rangery of Rangers, and could be a Fighter.
I can't remember for sure if Larian said anything about this. I'd say probably not. But I feel as if they may have said something about it.EDIT : oh, yeah, from the
FAQ in this very section of the forum.
Can I change the class of the origin characters when I recruit them?
Not at the beginning of Early Access, but we are planning to provide that option later down the line.