It would be nice to have the ability to file quests as 'irrelevant' in the log. I suspect that simply declining / abandoning them via the log might be game breaking if you deleted a quest on the main arc or whatever.
On the topic of railroading, what annoys me is not so much the quest log being stuffed full of things I'm not going to do, but the fact that I can't tell various characters to take a running jump and then back it up with force. Classic example is when you talk to Delphine, and she claims something about if she wanted you dead you'd be dead already. At that point, I recall quicksaving and then hitting her with ice spikes until she was crawling around on the floor begging for mercy. However, she can't be killed as she's 'essential'. In this case, it should have been possible for the player to kill her, then look at the map she's drawn up (its on the table in front of you ffs) and go to Kynesgrove based on that. Perhaps also find some of her notes in the chest nearby, allowing the main quest arc to continue.
Sometimes I wonder if the writers actually think things through. E.g. in the example given, Delphine is well aware that Septim, a dragonborn, basically conquered the whole of Tamriel based on his power as a dragonborn. And then they have her mouthing off at your character despite the fact that she should be aware that theres a good chance he can kill her effortlessly. She's even taken him into a hidden room where she could be murdered without anyone realising it... talk about stupid, especially for a character who is supposed to be cautious and a string-puller behind the scenes.
Similarly with the comments on the Daedra; whilst they're powerful, they don't have CHIM. Your character does, and damn right he should be able to mess them up. What would have been cool is if you broke one of their quests, they would periodically send their agents to kill you (much like the assassins who try to kill you as random encounters). You could even have their agents be massively overlevelled vs. the player, but at least provide the player the choice to act, and the consequences for so doing.
I think with Delphine it's a matter of superiority and faith in the myths of the Dragonborn. She believes what she tells you to do is what you should
want to do and is older than most players picture their characters so I do see her as perfectly in character. That doesn't make her likeable, but her knowledge of the Blades makes her valuable, at least up until the point you reach Sky Haven. Without Delphine, Estbern wouldn't help you and Alduin's Wall would remain locked away.
And yes, the Daedra have achieved CHIM. Or more correctly, they're in a state which does not require them to have ever been anything other than CHIM. The Dragonborn does not have CHIM, s/he is not omnipotent. The only time you can
really 'harm' a Daedric Prince is when you have been given the powers of a god yourself (Martin vs. Dagon, New Sheo vs. Jyggalag).