Hector, I agree with your assessment. I love the symphony as a whole. But it's those middle movements that begin playing inside my head whenever I think of the work, the passionate elevation of the Larghetto, the frenzy of the Rondo...
I like your analysis of the work's trajectory - the first movement is catastrophic, the last movement, after all that has happened in between, serene and positive.
Yes, the work does 'open out' in the end. You are right there.