I'm a little puzzled why you take issue with
@pemerton, who hasn't really said anything one way or another about good or bad play styles. I've read a comment or two from other people that MIGHT be interpreted as judgmental if you really wanted to take them that way, but they seemed pretty much in the realm of expressing their own likes and dislikes.
I think it goes without saying we all have somewhat different experiences, but it seems like you feel that other people pointing out those differences is somehow belittling your own, which I don't find to be the case.
So have you not read the posts that state that if the players cannot add to the fiction, it's a power play? That the DM is like a king and the players are peasants? That we aren't
really role playing because all we know is D&D. I don't have a problem specifically with pemerton except when he tells me I can't attempt to contribute to the thread by explaining why I don't want to add to the fiction of the world when I'm playing and it's never been an issue when I DM.
As to the 'thinness' you describe in the case of this Paladin... What would NOT be 'thin' to you?!?! I mean, a game in which the focus of the action (at least WRT that character) is on hunting down evil-doers as some sort of compensation for his thwarted sense of justice doesn't seem THIN to me at all! It might be only one aspect of a more complex character, so if that's all there is the PC might be a bit one-dimensional, perhaps, but maybe not. I can think of dozens of ways this can be manifested in play in terms of specific goals etc. However, at least in a Narrativist approach the most interesting kind of play might be testing him on it. Is he really willing to do terrible things to get revenge? Is he entirely sure that he's qualified to be judge, jury, and executioner? How about if his sense of vengeance demands that he go up against people he cares about?
That was one example where I actually had a concrete backstory. But it still didn't really give him goals per se, just an attitude. At the same time I don't really want to play a game with the narrative approach because I've never seen it well done in D&D (other games have other approaches and goals of course). Most of the time "moral dilemmas" are "here are two equally awful choices and you must choose one or the world ends" or similar.
On the other hand I have a character who's whole schtick is that he's a chef that goes adventuring. Other than the fact that he likes to eat and try different foods there's not a lot there. But he has a bad accent, a fun attitude, likes to use food analogies for just about everything. We have a lot of fun.
For a lot of people, their entire concept of a character is limited to race, class and usually a physical description. The character, if any, emerges during play. I don't see an issue with that.
I think there's solid RP potential, at least, there. I would think that if it came out seeming thin that was more due to the way the GM in this example (which you don't discuss, so we don't really know) approached the whole thing. If he just went on ahead and ran some adventure or other without this whole thing playing any role in it, then sure it may have amounted to a hill of nothing. That seems to me to be more a commentary on the GMing techniques in use than anything else (and again, to be clear, if all you wanted was a backstory to be mild color, then your GM was batting 1000).
Except that's pretty much what I want. Go on adventures, maybe save the day now and then, get the kitten out of the tree, tell bad puns, have a few laughs, inhabit a different worldview for a while. I did work with my DM to do a side story on how to get a ghost to move on that turned into a short story (I like to write them now and then), but that was just downtime activity.
But it's also in part because in that particular game we had 7 players and we could only get together once a month for a 4-5 hour session. There simply aren't enough hours of gaming to pursue everyone's personal stories.