I think I am guilty of most of what you dislike about Authors, Peter
And while I do agree that players should have a certain amount of agency, I also am strongly on the side of the "story"-driven adventures.
In my own defense, I do tend to write somewhat more closed-off storylines. I personally like the idea of Heroes becoming involved in a situation much bigger than themselves; having to survive when life is falling apart around them. I personally feel it gives a certain edge to an adventure. As to player agency, I do agree that a Player has to feel like they are involved in the story, and that they are experiencing something. That said, I am also in favour of LIMITING how much a player can do because I am a sucker for realism. In real life, the King of a country is unlikely to blindly take the word of a bunch of (often) foreign meddlers who he has just met, so in many ways I find adventures where you can massively change the politics with a single skill roll as breaking my immersion in the universe.
I also find that by limiting options in an adventure, it forces people to be more creative. If you simply allow people to do whatever they want in order to force agency, there comes a point where you can push the experience from RPG to a pen-and-paper version of Goat Simulator: Fun and amusing, but lacking substance (NOTE: This is an extreme example meant to illustrate, not to be representative). I am also a fan of trying to keep a narrative power-curve going, where Tier I characters can affect the world around them, but not as much as a Tier II could, and neither of them as much as a Tier III could. Though I know that PCI and Henry got a fair amount of grief about the level of Player agency during the Crusade (some from me, I admit), looking back on it it was as close to 'perfect' a representation of the 'power level' of the world that a Tier I character SHOULD have access to. Now that we're in Tier II, we're rubbing shoulders with Prelates and becoming involved in a brewing conflict in the Blessed lands as our own people instead of just as soldiers in a war. Next Tier we may be actively seeking out conflict and 'righting wrongs', and the one after that we may once again become "Champions of Light".
As for adventure length. . . well, as you say, it is very hard. Of my three adventures that have been released so far, one I found was too short, and one had to be split up into a two-rounder. Being able to condense an experience into a 4 hour timeslot, allowing for Roleplaying, fights, and plot is hard, and not a skill I have admittedly mastered yet. That said, I am going to continue to pelt my imperfect adventures at PCI in hopes that practice makes perfect