I don't see why the big scale bothers you, It's scientific, And It's more scientifically well-explained that the short explanation. You don't have to see everything in front of you to make sense of it, Sometimes you have to use your intuition and imagination to understand large-scale concepts.
Sorry, I didn't see this before but I want to comment on this because it touches on another area where I think the endings failed terribly.
One big problem I have with the reapers in the endings is that they are deprived of the incredible power and scale, they represented throughout the trilogy. First of all, they are leashed by the catalyst, who somehow at the same time is supposed to represent their combined intelligence (how that is supposed to work, I don't know but let's move on). Even worse, the revealed motivations of the reapers show that for all their age and all their grand perspective, their thinking process seems to be severely limited (later, in the Leviathan DLC, it was explained why that is but that doesn't make the intellectual castration of the reapers any better). As their purpose, they project a problem that they never actually observed, predict it as being the truth and then the only "solution," they can come up with is stagnation (the cycles). They seem to severely lack in both imagination and foresight and they seem to concentrate on a really small picture, given their sheer power. Again, Leviathan tells us why that is but still, I am bothered by the fact that it is.
What happened to "we are beyond your comprehension"? What happened to "you are fumbling in ignorance"? The problem they are trying to "solve" in a pretty stupid way is not that complicated in the end and furthermore, their premise is flawed and they seem to be too stupid to even see it. Before the catalyst conversation, I was awed by the reapers. After it, I kind of pity them. That's an anticlimax right there.
Say what you will about the dark energy concept. Yes it was unfinished, yes it needed a lot of work but at least it had the potential to create a plot that would have lived up to Sovereign's smack-talk from back in ME1. The way things are now, which essentially boils down to the fact that the reapers are afraid of the future, that does not live up to the expectations I had.