Well I don't disagree with anything you said there other than the part about forgetting about the foregone conclusion. That part didn't work for me. The only time I was at the edge of my seat during that film was in the final Mystique/Magneto/Charles confrontation with the whole world watching. While I knew the future would be undone, I had no idea HOW, and therefore had now idea which way that confrontation was gonna go. So that was a great suspenseful moment. And I enjoyed the movie quite a bit (my favorite X-Men to date), but it definitely wasn't the visceral experience for me that it was for you. The X-Men movies have only ever managed to get me invested in one or two members of their ensembles at a time, so I'm never that into most of the mutant ensemble action. So many of the mutants seem totally disposable to me, like they just exist to show off their powers then disappear.
Weirdly, the Avengers was more visceral and intense for me just because of the adrenaline I was getting from the sheer joy of that final battle (and the helicarrier sequence). I was just so pumped watching these epic comic book splash pages come to life (featuring a full ensemble of characters that I was invested in), that I too was on the edge of my seat...in a totally different way, haha. Which is why I've said before, The Avengers was like a rare, once-in-a-lifetime theater-going experience for me. The moment I walked out, I immediately wanted to turn around and buy another ticket to watch it again (and I totally would have if it wasn't an advance screening, lol). Days of Future Past was a damn good movie, but it was still just a movie to me. I didn't come out with my mind blown or the urge to buy another ticket right then and there. Was it a more effectively dramatic story? Of course, but I've seen plenty of great dramatic stories in my time, some of them even featuring superheroes...but I've rarely experienced anything in a movie theater like The Avengers. *shrugs*