I can't see there being a prologue, and a Mind Flayer ship tutorial, and a beach section and more tutorials. That would make the early game drag on.
I can't see Backgrounds being more than just bonus skill specializtions, because they will never match the player's ideas.
Heaven forfend our RPG takes its time building character mood and setting...
That's what the actual game and companion interactions are for.
NPCs gradually opening themselves up to you is way better than you just being infodumped everything within the first minute of meeting someone.
In the event that you're referring to the player playing as one of the Origin characters there's going to be an introduction video to the different characters in the character creation menu. This should be sufficient to give you an idea of who the character is, what their personality and what their motivations are.
NPC's gradually opening themselves up to you, and the plot of your adventure slowly unfolding as you go are very different things from what I'm talking about. Your character, the setting, and specifically the custom MC who doesn't have the benefit of having a bespoke backstory to slowly incorporate into the tale, are.
A Prologue doesn't need to deal with anything pertinent to the plot of the game, but it can go a long way to set your expectation about what kind of world we're dealing with, as well as your custom character's place in it, heroic or not.
I'll use the two previous BG games.
Baldur's Gate: you get a VO setting the stage, you're an orphan living a monastic life with your foster father, you go around meeting people, allowing you to get a feel for what your character is like and introducing you to the world, this ends when you're waylaid by some baddies who murder your mentor and set you on the path of adventure.
Shadows of Amn: completely out of left field after your triumph at Baldur's Gate we meet our hero after he's been captured by a mad scientist, who subjectes him and his friends to torture, after an indeterminate amount of time you escape and rescue (or not) some old companions, Irenicus's dungeon lets you establish what kind of character you are, tells you this story will be incorporating more darker elements into the high fantasy before putting you into a completely foreign city.
I know people like to vent at having to play through Irenicus's dungeon but that only really became an issue to me after I understood your character is only ever going to be a cipher in this game, so your choices don't really matter, and because at that point I've played the game so much I can go through it blindfolded. Shadows of Amn had a tutorial too, which deals with your capture I think, I only played it once well after finishing the game multiple times, so I can't comment.
Compare with BG:3, you awake in a Illithid pod, are implanted with a tadpole, then go on an adventure to get rid of it. With the origin characters it will no doubt be different but if you play a custom character don't expect to have a personality that isn't established by other characters.
