Of course the hirelings need to be customizable! Offer a 13th choice for all of us who freaking fucking love to customize characters (and with the EPIC and extremely elaborate character creation menu that the full game will have at launch - how can anyone NOT love to create their own characters? How can Larian even think of not giving us the opportunity to go nuts with all the variety they offer us? )
I don't mind custom companions being completely silent and not offering up their opinions all the time, just as I don't mind that my main character is silent - because I AM THAT CHARACTER! It's thoughts are mine, I give soul and life to that character - just as I would with the custom companions. This is an R P G. Role Playing Game. We play the roles of our characters, be it one or more. That being said I don't mind having one or two of Larian's companions in my group to offer more depth and lore to my game, I would never go "full custom", but I like having the option to mix and match.
It's actually very simple; just do like they did in Pillars of Eternity 1 and 2 (and in so many other CRPG's). These are older games with far smaller budgets. To me it is just a quintessential part of any CRPG, and I can't even fathom that with a game of BG3's dimensions (everyone is shouting "GAME OF THE YEAR" even before it is out) we are even having this discussion.
It is weird how BG3 tries to do so many things, but can't feature such simple features like rolling the highest stat in the group and just making 4 TAVs. I am confused by it. Not even day and night cycle or at least some different weathers.