The Trevelyan Inquisitor's drunken aunt is meaningless in the context of the game, the tournament won by the Cousland Warden before the game even begins is meaningless in the context of the game, changes to Jensen's appearance based on what augmentations the player chooses to get would actually reflect the decisions the player makes in the game giving them far more significance to the player.
It would reflect those "decisions" in the most non-sensical manner possible. Skyrim did something similar, where reactivity meant characters whispering "Hail Sithis" in passing. Of course, luckily, Skyrim didn't have to sacrifice the character creator to do so, which would be more than likely with the Jade Empire approach. It's actually even worse in this scenario since many of Adam's augmentations are under the radar and again given HR's overall setting, means virtually nothing compared to the fact that he's augmented in the first place.
Does the Inquisitor's drunken aunt (that you never get to meet and has no effect on the game whatsoever) change how other character's react to your character? How about the tournament? Apart from that one off reference in the origin story how does it effect how the rest of the game plays out?
It's odd, because if we change the Inquisitor's drunken aunt to "blank slate protagonist", you get the exact same argument.
Of course, best case scenario involves the game giving the player at least some measure of choice in that background. Which coincidentally Dragon Age does.
You are trying to argue that visual changes that reflect the player's choices are meaningless yet useless and inconsequential tidbits that the player has no input in and are meaningless to the player are somehow vital to the roleplaying experience? Surely even you must realize how stupid that sounds?
Role-playing typically involves playing an actual person. People have experiences. Unless you're suggesting that in your day to day life, in conversation, you spend more time talking about other peoples' appearances and never (even once) talk about your past experiences? Surely even you must realize how stupid that sounds?
Why is it absolutely vital that the player character gabs about their past? Not everyone is so eager to talk about their past at any given opportunity and some don't like to speak of it at all, one of the biggest flaws of Bioware's recent games is how they place far more significance on events in the past than events in the actual game, if the events in the characters past are so interesting then why not just base the game around them?
Again, if that's the case, then please follow through on the thought experiment. Show me, by example, how a person conducts their day to day life without referencing any of their decades of experience, ever. You're certainly eager to defend these sorts of role-playing concepts. Who knows? Maybe you can actually pull it off. But even if, by some miracle, you did, it would still represent an incredibly narrow range of role-playing options, to the point where the implementation simply isn't worth it.
That's what makes your argument here so non-sensical. Sure, not everyone is going to give you a heart-throb story about how their father hated them and they can't ever function again. That's potentially feasible. Unfortunately, your argument takes that premise and goes off the deep end, to the point where a character may as well have been born the day the adventure started.
That would be the key advantage of the Inquisitor's Great Aunt story. The story itself isn't particularly great. Of course, in a best case scenario, the game would let you see what the dialogue was before you chose it. What's important is, at the player's behest, to be able to reference that background as a relevant experience, if the player wants. Or a better example, Josephine asking the player what he spent his youth doing. But according to you, those and the Origins are meaningless experiences to the player, but (somehow) a non-existent background matters more in that regard.
While a backstory and past events can be useful in explaining the motivations and demeanor of other characters in the universe when it comes to the main character who's motivations and demeanor should be the player's to decide it is best to leave the backstory blank for the player to fill in the gaps, sure it will never get mentioned in the game but that is one of the concessions that must be made, it is still a far better alternative than forcing a pre-defined backstory on the player.
If that's the case, it's certainly not supported by the reactivity argument, which indicates pretty well why the blanked slate protagonist's lack of reactivity is a problem.