Well, at least one backer (named Hiro Protagonist II over at Obsidian forums) at that tier said he actually had no input on his NPC's story whatsoever (beyond just the name, presumably, as that NPC is called "Hiro").
Whether that's the case with the other backers is another matter, but I'd be surprised if it isn't largely Obsidian's work.
I backed that tier and can confirm that I had very little to do with my NPC.
You chose a name. In my case I made up a generic fantasy name and hoped that it might fit. We weren't supplied any naming conventions of the various races and cultures so it wasn't very easy to do that.
We had to fill out a brief character description (general traits). Pick race / class -- you couldn't choose no class for example and be simply a farmer or librarian. You could pick basic appearance: skin and hair colour, colour of clothes. That was about it.
I would have liked to have some basic details about the world so that I could have tailored my NPC to fit. Since that wasn't possible I just described myself in the most mundane, boring terms. My description was only a couple of short paragraphs as I don't recall that text field being huge. I ended up making a vanity character, basically. But it was impossible to come up with something interesting that would be unobtrusive with no information. My description didn't include any overblown power fantasies or anything like that. I just described my basic, real-life personality and an interest. I felt it would be really annoying to be all, yeah I'm a werewolf who lost my angel wings who's the heir to a royal kingdom and could easily blast a hole in the sun with my supa speshul magick omg.
We weren't told how these character sheets would be used which made it doubly tricky to fill out. We had no indication from Obsidian if we were going to be used for vendors, enemy NPCs, quest givers or simply flavour text (as it turned out). I had no idea if you'd be able to speak to my character or not for example.
So yeah, my character story was a complete surprise on almost every sense. But I'm not displeased with how my NPC turned out. Mine was kind of hilarious.
If they do that again there's definitely improvements that can be made. Double Fine vetted backer names and descriptions for Massive Chalice for lore friendly stuff. They'd warn you if you weren't. You could then choose to either amend your content to be lore friendly or be included under a non lore friendly segment of names that could be disabled by the player. Players could then easily avoid things like backer content with names like Hiro Protagonist and Sturm Brightblade and many of the obnoxious memorial stones.
Tldr version: If you hate any of the soul stories and think they're super cheese or badly written, then unfortunately that's on Obsidian. We had next to nothing to do with them.