That's exactly what they felt like.
Which is why I LOL at the assertion that MP adds to SP
That's true and I don't think there is anything at all wrong with it. In fact, I think it's a great idea to use these recourses and give them to SP players as well, especially since the cost is minimal. As someone who doesn't play MP, I was happy to get a chance to see the maps and get to have some small missions on them. I wish they had also made N7 missions for all the add-on maps that MP got later (although I see why they could not do it).
Even though this may not have been clear from my earlier posts, I have absolutely nothing against small throw-away missions (also liked the N7 missions in ME2. However, while they are definitely a nice addition to the game, that same game still needs proper content in the main quest (and also in more elaborate side quests). It's why I don't complain about the fairly repetitive witcher contracts in Witcher 3 because they were there in addition to a lot of main and side constant that was very carefully crafted to tell brilliant stories. If I can get both, well than hurray! If I have to choose, I'd loose the smaller side content first and rather keep less missions with a more fleshed out story and characters.
And this was the problem of ME2. I am not complaining about the addition of N7 missions, I am complaining about the lack of careful story telling in the main missions.
We see what happened to Horizon. Why do we need NPCs telling us about what we saw?
It's not about them telling us what we saw, it's about them telling us HOW they saw the same thing from their perspective, how they react and to make us react to that in return. We don't know Horizon, we don't know anyone there (except Ash/Kaidan and they are not connected to the colony or the attack at all, we might as well have met them on the Citadel, it would have been the same). We don't have a relation to the place. We are just there to fight the collectors and to save faceless and nameless people. If we had the perspective from someone who lives there (and who comes across as genuine, so not that mechanic) and who can relate their much more connected and in-depth feelings and concerns to us, then we are no longer just there for the enemy or a number (of people) but those people can (if it's done well) get a face that might actually mean more to us.
Imagine that in Dragon Age Origins, you'd arrive in Redcliffe just before the attack starts. You get one villiger coming up to you, quickly explaining the situation in two sentences and then you get to fight the darkspawn. This is perfectly doable (and in fact, 90% of video games would probably have done it like that). You could even keep the mechanic where you fight with the villagers and you can loose them if you are not careful. You see the same, get the same information and ultimately have the same outcome. But it simply wouldn't have the same impact because you don't know who you are fighting with or what the relevance of that the villige you are defending is beyond a quest goal and maybe a tactical asset for the war against the blight.
What I am saying is that this exposition is important because having a context to what you fight for or to who the characters in a plot are increases the intensity of the fight/plot, it's simply more effective storytelling. Yes, you CAN just show the bare minimum of important stuff (as was done on Horizon) to convey all the relevant information. But now you are thinking in terms of what's necessary, not in terms of what's possible. I don't think this is a good way for a writer to approach his own story. As a writer, you have endless possibilities, it's up to you to come up with the best way to portray the story that you want to bring to the audience. If you want to write a story about fighting a force that relentlessly abducts defenseless colonists, is the best way to approach this really to show exactly one of them and to have that one barely even talk about the issue that your story is about?
I know that video games are not known for their great story telling as a whole and may have other priorities but BW especially marketed themselves as being special in the industry exactly because of their expertise and focus on this facet of games. I play their games because of I want the experience to be told a great interactive story while playing a game, so if they screw it up, it irks me more than if it happens in other random games (and it happens a lot).