I don't even need to line by line the above, because you know I agree, more or less, but as I was never comfortable with the premise I am far less inclined to write it off and move on (but we must, for the future, etc. Yeah, that). You've also managed to highlight, much better than I could, exactly how much drama was simply left unplayed at the end of the whole thing (and, by extension, has yet to be played out). A brief encounter with another soul bound to walk a destiny separate from your own... It's poetic, to be sure, albeit in a much more somber and tragic way than it was played on-screen, but...

I still think Allag has an bigger endgame than simply "hope for all mankind," and that the Crystal Tower will factor into it, but not necessarily as it was intended to. Nothing supporting that except this chill that runs down my spine every time I look at it, but we'll see where it goes.
I also like to think that we're not quite done with Allag yet, mostly based on the cliff-hanger cutscene at the end. But I doubt we'll find out anything for a long while yet.

For an ending about hope, I found it to be rather depressing...
1: Unless we blast the doors down, we're probably never going to see G'raha again.
2: By the time he wakes up, Revenant's Toll will look like Academia.
3: Who's to say the people of that future will even be friendly to him?
4: If the tower can only be controlled by Allagan royalty, did it sort of slip his mind in his rush to seal it up and sleep because his gift was only temporary, that he forgot it was only temporary? It's going to expire one day, just much later. But it will expire and then the tower will be left as nothing but a pretty landmark again.