Your reasoning for the lack of critical and journalistic outrage over the ME3 Ending seems to largely boil down to the fact that reviewers have a tough job and hard and fast deadlines, which makes it difficult for them to delve into reviewing something so time-intensive as story. While the pressures of the job are doubtlessly true, and your point about mechanics being easier to critique than story makes a lot of sense, I'm not sure that I entirely buy the argument that reviewers should be given leeway for missing a major failure of a game just because they didn't have enough time to fully explore it.
In my opinion, a broad, general review of a game that only covers the basic gameplay elements and mechanics is a waste of both the writer's and the readers' time. If anything, game reviews need more "nitpicking," not less. If, while playing a game, you find some little quirk or plot element that continues to bug you throughout your playing experience (or in this case essentially negates your previous 100 hours of story decisions), chances are that 1) you're not the only one and 2) the people relying on you for an appraisal of the game probably want to hear about it.
In a normal career if you present a cursory and incomplete report and give the excuse of "well I didn't have enough time" or "this is the best I could do because I was busy," chances are you're going to be looking for a new job rather soon. Even if these excuses are entirely truthful and do in fact justify your incomplete work, that does not excuse you from your responsibility of doing a thorough job. And I doubt the intention of game journalists is to marginalize the importance of story in gameplay; if it's an important part of the game, I want to hear about it, regardless of your time constraints. It's easy for me, having no experience with their career, to give some general (and obviously naiive) advice like "work harder on the review" or "spend more time on the game," but honestly, that's what they're being paid for. :/
The fact that the single glaring flaw in ME3 was largely ignored by most game journalists does not, unfortunately, make me pity their lot in life, but instead makes me question, if not their integrity, their dedication to their craft. And even if we excuse reviewers for all of these reasons, how do we explain those people writing weeks after the fact who still miss the point (like Yahtzee and Bob) whereas journalists like you (even if you don't consider yourself one, I do) are able to perfectly capture and explain why fans are truly angry with such a great degree of tact and detail?
Anyways, it's almost eerie how exactly you matched my reaction-over-time to the ME3 ending.