Really, you felt the same way about Edér when you started the game and when you were done with it?
What about Aloth? Did you feel the same way about him too?
Durance also tells you that Magran is a bitch and he's mad at her right as you meet him.
Eder's only significant development in the entire game happens during the encounter with Maerwald in Act 1. Everything else - his back story, his prior beliefs, his loss of faith - he tells you almost immediately. For thematic purposes, his quest to find out what happened to his brother is ultimately futile, and after whining about it briefly, he shuts up for the rest of the game. That's his entire narrative. What am I suppose to feel?
As for Aloth, he DOES change through the course of the game due to having to come to terms with the other soul living inside of him, but his story was so silly I dropped him as soon as I was able to. That's my problem, though, and he IS an exception to the rule, in terms of narrative structure. A pity that it's played for laughs.
Durance tells you that Magran's a bitch immediately, but does NOT reveal to you that: 1) he made the Godhammer 2) he did not abandon Magran; rather, Magran abandoned him 3) he fears HE was in the wrong, and so his anger at Magran was actually a form of guilt. Completing his personal quest changes Durance's character completely, since he is now certain that Magran played him all along, and that his loss of faith was justified, and not a consequence of his own mistakes. And that's with most of his content cut, by Avellone's own words, so you can just imagine what other developments there would've been, had that not been the case.
Both Eder and Durance's narratives are supposed to be subversions of common CRPG cliches, in keeping with the themes of Pillars of Eternity. For Eder, it was the idea that the underlying facts must reveal themselves eventually - subverted by them not doing so. For Durance, it was the idea that a priest who loses his faith, always finds it in the end - subverted by him rejecting it altogether. As such, the ideas behind the characters aren't the problem. The presentation is what distinguishes.
As a side comment, Tyranny seems even worse at keeping character development going throughout the game, rather than throwing it all in at the beginning.