Maybe what you could suggest is that you can change your companions looks to better fit your tastes like you can do in DoS2. That would better fit your demands because making companions that are liked by everybody is a pipe dream. I think you are just talking about your personal preferences.
"I want to be able to initiate a dialogue with my companions" or " I want that particular XYZ rule or spell to fit the 5e ruleset" would be fair suggestions but something in the way of "I want the companions to fit the way I portrait a mage and also I want them to look and behave in a way that I like" seems a little silly to me, no offence. Because if you ask 1000 people you will have 1000 different answers and I do not think Larian (or any other game developer) has the budget or resources (or the will) to do so.
we had to be able to choose which role they'll play (classes/alignement/...) => they have to be designed to suits with nearly everything => their design/backgrounds/personnalities are limited to random/usual things.
I think their class is fixed? Even if you pick them as an origins character.
I think your companion classes are fixed. When the Character creation UI is showed in the first gameplay, Sven could change the class in his custom character, but when he changes to an origin character like Shadowheart or Astarion that option disappears.
That´s ok in my book. That way you can fine-tune his story and background.
