Well, I consider the Origin as the reason why Duncan recruits us. It proves our mettle and suitability for the Wardens. As it plays out, it truly is blind luck that we stumble into the scene with the Divine and Cory. And then we still have to go in the Korcari Wilds and fight off darkspawn.
As silly as the cutaway scenes with Loghain and Howe were, they did put a face to our antagonist and what he was up to while we were in the field. And sending Zevran after us, the soldiers in the tavern tricking Warden supporters, the bounty hunters in the Frostback pass and guards at the gate, hiring Jowan to poison Eamon, allying with Uldred, all the influence of Loghain against us.
Killing a few nobles/soldiers/treking through a small dungeon/whatever other minor task is in the origins I didn't play is not a reason to be able to lead an army. Neither is killing a few darkspawn. It's blind luck that Duncan saves you at the end of your origin. Both protagonists only become the protagonist due to luck, in fact the other origins still happen if you don't pick them, the character just died at the end because Duncan wasn't there. So I consider there to be equal part luck.
Cory also takes action in the game. He attacks Haven, he attacks Celene, he turns the wardens against you. I hated the cutaway scenes from origins, so I'm glad those were removed. I don't want the game giving me knowledge my character doesn't have.
Origins sure was a generic "defeat the ancient evil hoard" (though I'm not sure why you brought it up) BUT Origins had a lot going on with the blight as a backdrop rather than the sole focus like in DA:I (and I'd argue that Loghain was a lot more of a character and a lot more interesting than Corypheus). In Origins we were introduced to this whole new world, got to learn about different people and cultures and places not by reading a note on the ground but by going to those places and interacting with the people there, participating in their problems. I loved it
. Through the origin stories we got to see where our character came from and experience a little slice of their everyday life before they became a warden rather than being told "you were part of a Tal Vashoth mercenary band." Warden treaties or special magical mark, both are boring. I don't want to be a special snowflake chosen one, I want to fight for and earn everything I get.
Why wouldn't the game expect you to care about the Divine? It beats you over the head with her death the first third of the game, two of your inner circle were her advisors, your organization was founded by her, and she died to save you. You should care about her. The game should have developed her if they were going to use her as a major plot point.
Cameo was the wrong word. Blatant fanservice inserts would be better. IMO the game would have been much better off with all new characters that the devs had taken the time to flesh out and develop. Using so many returning characters from other things seemed like a blatant excuse to not give them time and attention but rather rely on previous development. For example, people that read the books might have accepted Celine as this brilliant strategist and master manipulator as characters in the game tell us she is (though without giving examples) but she never actually does anything clever. She doesn't even notice the obvious mobs of murderous venatori in her own palace.
There's exactly zero tension about Cassandra possibly executing you in the intro. For one the game wouldn't be an hour long, and for another, we already knew Cassandra becomes a companion before the game even came out. If this had happened late in the game it would be a different story. She thinks you lied and betrayed her, she attacks you and you have to kill her or she leaves your party. By that point you'd already know her well and her fate would be up in the air. You also don't do anything to convince Cassandra that you're trustworthy. She hears a convenient magical recording of "somebody help me!" and "what's going on here?" which was enough for her to come to the conclusion that the Divine called out to the inquisitor specifically and that they must be innocent. The hand potentially killing you likewise had zero tension for the same reasons. We all knew that wasn't going to happen. (compare to Trespasser where it was uncertain, kept escalating out of control, and there was a real possibility of death). So yeah it was "climb a hill and fight some generic monsters." Snooze. The only interesting thing to come out of that intro was the possibility that Andraste saved you. Not the mark, not the breach, not the unknown characters that died offscreen before the game started, not the generic demons or the long list of repeat characters.
I brought it up because people seemed to be saying the plot of origins handled everything much better compared to Inquisition, so I assumed that's what things were being compared to - sorry if that wasn't the case! 
I disagree about Origins having less reading though. I've been replaying and there are a lot of quests that are just writing. The chanters board/mercenary groups/mages etc are all just pure text. And so far in my game they have all been "go here, kill monster", or "collect items", or "go here, talk to generic npc". Maybe they get better as the game goes on? - I honestly forgot these things existed before I restarted... There are a lot of other quests as well that are just reading notes.
And the game does not want you to care about the Divine. The fact that other characters who did know who cared, does not mean that you, who never did is supposed to. Her death is a plot point, because of how it affects Thedas, not because her death is supposed to make you feel very sad.
I'd agree it would be better if they didn't reuse characters, though that might just be because they used characters I never really cared about (Leiliana, Cullen).
I don't think Celene is supposed to be seen as brilliant though. If you keep her in power, the game tells you how precarious her situation is after the game. She only stays in power because you put her there, and both the game, and your character (in Trespasser) outright state this. She may have used to be good at the Game, but not anymore.
So you feel any character/plot that threatens you in the first 100 hours of a game is pointless, because the game won't kill your character at that point? I guess thats technically true, but a game requires a certain suspension of disbelief. I found the interaction a lot more interesting than I would have talking to a few generic mage/templar NPCs at the start of the game.
Eh, evidently the game didn't work for you. It worked for me and a lot of other people though. Can't please everyone, and I don't think we are going to agree on this. 