The dream sequence struck me from the beginning as you mention.
You've been painfully slowly chasing this child in your previous dreams, and so you come to find a child in a frustrating perpetual struggle oddly reminiscent of my own dreams where I'm powerless to help someone/myself and feel as though I've been stuck in molasses.
Some other things to perhaps consider...
1) Shepard has already been converted/indoctrinated after the laser zaps him/her. The two husks represent your squad members, and you mow them down with ease in a moment of surprise before going up against some foe with a reasonably good weapon who generally has no problem mowing down quick convert reapers.
2) You had no pistol, and certainly had a better one than that by that point in time. Your teammates who were on Earth with you show up in the crash sequence. Why would the Normandy be that close to the relay to escape anyway? As someone else mentioned, your armor changes, and you spend the whole thing limping. And how would Anderson possibly be there at all? Makes no sense.
3) Stargazer. Clearly, this story being told about the ending is a legend. They are prone to mistakes and common acceptance of whatever permeation was passed down generation to generation.
4) The "From Ashes" DLC directly butts heads with this. According to Javik, the Citadel was created by the Protheans for use as the crucible, but was conquered during his lifetime. When shown in the game, in it's closed state, it's clear the point is to aim it at something or send a beam at something. Even the shape of the citadel from the beginning shows what very much looks like a mechanism for magnification or aiming at it's center. This of course, does not explain the keepers, and what they would be doing appearing to tend to the bodies in the "aboard the citadel" thing.
Despite my disappointment at the ending and how lazy it looks from my first play through.... I'm really hoping this was the real reason why they needed to release From Ashes day 1. This of course, supports the "game was not complete" angle. But it seems at this point they are doing what they can simply to cash in on the franchise and go about their merry way.
But the end result it left me with, is that my loyalty to the franchise, and my plans to go through all the games, seeing how my decisions affected the ending are all rendered moot because a number of those choices were ignored in the entire last game. For instance, I did everything in my power to keep Udina from power, because I knew he couldn't be trusted. Spent the entire ME2 first game with default choices, accepting that humans ran everything. (I don't know if that's actually the case when you play through with what you selected).
I also am left to wonder if it is Earth, whether they will be battling with other stranded civilizations some time from now, when everything has been relegated to myth and legend. These species probably can't even breed without the help of an asari.
Another something to consider, what if the crashing of the Normandy shows exactly what the reapers intended to do? Fracture the civilization, handicap the technology, and force them to get back to the same point again. Even if many reapers died, it would seem they would spend much of the rest of their times going around, wiping out other civilizations in other places.
The inevitability of master vs machine vs machine master wasn't exactly compelling the rest of the way through, but I still find myself, even being able to rationalize the dream sequence, extremely disappointed at the laziness of the ending of the game. And now, with only some "global whatever" score mattering to the ending, I have no desire to play any of the games again, despite my love of the lore and the universe that was created. I'm going to finish the game again with a higher war score (first time through was about 2800), and see if I notice anything better...
No, this is a case of Fonzi vs. Shark. Baffling to me how the entire series could get my buyin up until the very ending.
It seems to me like if you saw an injured animal. You take it under your arm, give it every bit of attention, nurturing, etc that it needs to recover. You make it your personal mission to make sure it survives (the child parallel seems good here). One day you come home, just in time to watch your SO shoot the animal as you pull up to the drive. All of your questions are only answered with "well, it's dead now."
Edit: Some of this stuff was stated otherplaces in this thread, but I read the OPs thoughts and am giving my responses to those.