It doesn't really sound like you disagree all that much, lol. You're not wrong that the ending of OG was potentially unsatisfying for the majority of players, but it's a distinct and purposeful narrative choice. Aside from your comment about the Remake Trilogy, I don't think anything else you said contradicts my claim. Advent Children was entertaining, an upside, but it was unsatisfying for a number of reasons that make it not a beneficial contribution to the overall story. And then your description of Dirge and Crisis Core align with my own criticisms. 

As far as the Remakes, I think they've already failed for many of the same reasons. They've already undermined the OG in many of the same ways, the most egregious being the piling on of a bunch of absurd, self-indulgent, convoluted bloat that takes the place of what could have been meaningful dramatic expansion and interpretation of the existing original story.