your character doesn't lack distinguishing features and they're not completely "blank." What I've noticed in my multiple playthroughs is that the selections you make at the start of the game are actually fairly impactful RP-wise, much more than I expected them to be. If you're playing as a Githyanki you'll find several skill checks that you simply bypass because your whole species has dedicated themselves to hunting mind flayers, so naturally you know quite a bit about them. If you're a rogue you'll immediately comprehend what's happening when you encounter someone trying to swindle you and be able to call them out on it. Your background, class, and selected skills *do* have an impact to an extent that I certainly didn't anticipate coming into the game..
I'm playing with my spouse, and we tend to try for different skills so as to compliment each other; and this certainly does mean that one of us or the other will have dialogue or action options that the other does not. So yes, I agree that the choices one makes certainly do flesh out later.
I would like to see MORE of them having an effect. Ideally I would like to see... oh let's say at least 3 skill/race/proficiency potential options in every encounter. Also at least good/evil and maybe chaos/law type options. Also humor/dour options. Yeah.. then I suppose there would be complaints that there are too many choices.
Can't please everyone I guess.