Which confusion??? Pre-made avatars work since the Infinty engine games. I don't understand the problem after all...
The problem is that you need to understand what a game "Divinity".
This game not "Diablo 3" and there is no target level up your character as quickly as possible and stronger.
Game "Divinity" mimics table games , so here aim to play your character, and therefore should be full immersion .
But when you are plugging into the game the other person who created two characters ( Knight and Witch ) and they are avatars (one " hippopotamus " and the other "city " ) in this circus to understand who says what and who your character?
All decisions of the studio "Larian" must start not from the infinite functional , and the idea of the game is aiming ...
I still don't fully understand your point I fear but I will try to answer to it nevertheless...
First, I don't speak about Diablo, I speak about Infinity engine games. If you don't know what that is please look it up. There is a big difference between them. D:OS is in fact much like the classic Infinity engine games in many aspects....
Sceond, my suggestion to be able to include own portraits would add more flexibility and immersion without sacrificing the artistic look and feel of pre-painted portraits. You could just create your own portrait in photoshop fitting the character you created at the beginning of the game or took one from various sites on the internet or even from other games (like the mentioned Infinity engine games...)
And of course in co-op you have to take whatever portrait the host created for his avatars (that's just one of the effects of the hop-on, hop-off co-op concept). The only option to prevent that is to start the whole campaign in co-op together which allows you as the one not hosting the game to choose your own character and fitting portait.
