No. No Shepard didn't. Anyone who thinks that the breath scene is Shepard dying doesn't know how "stuff" works...
I've read all the "arguments" for why the endings were bad, but it all seems to distill down to "they didn't end it the way I wanted". That's subjective.
TL;DR: Don't bother. I won't be swayed. I love the endings and that's that.
Let's put it this way; inductively, you're right. Technically speaking, a lot of people didn't like the ending because it wasn't the way they wanted it.
But that in itself is a subjective statement. WHY did people not find the ending to their liking? THAT'S The kicker statement.
Some people, like iakus, don't like the ending for reasons such as it not being 'morally happy' or 'ethically acceptable' since the ending scenario introduced an a new perspective that was much more alien and divorced from the rest of the franchise and addressed tangential themes that were divorced from the more conventional good/bad themes and presentation prevalent in the writing by BW (I suspect they want to change this, but too many people are too hung up on the idea of being a paladin/paragon and getting their power fantasy). They're more concerned with the outcomes and actions taken in the ending rather than the actual perspective and rationale presented by the Catalyst.
Those people, I feel, should not really be catered too.
On the other hand, there is the issue of presentation and technical narrative. The ending to ME3 was very weak in that aspect. It was hamfisted writing that presented a limited ideology within the argument presented by the Catalyst. Narratively, it doesn't make sense. Which is a flaw. There is a lack of reflection and insight, compounded by a hamfisted and biased presentation of the beliefs that the writers themselves are beholden too, and they have essentially committing their final perspective on the issues presented by the ending as the paradigm argument. They offer no ability to have a reflection on the arguments presentation, logic, or reasoning, and (despite later statements) leave little room for interpretation on what they consider, nay, force to be the ultimate solution to the problem. It's biased writing. It's lazy writing, made evident by the lazy presed now ntation. As well, there was a lack of development time, and a lack of characterization of the final options.
I agree with part of your statement. But it's a bit willfully ignorant to say that you're unable to be convinced that there were any flaws in the writing of the ending, and the blatant generalization that everyone who sees a flaw is a complainer who 'didn't have the story end the way they wanted it too'.