Imagine that the final Gharihim battle IMMEDIATELY transitioned into the Demise confrontation. Demise is summoned and snatches you away into his realm to do battle. There you are, probably minus a potion or two from the previous battle. Adrenaline is still kicking from the horde and the escalating (or really, descending) fight with Gharihim. Then Demise arrives, ready to pummel you with his massive battle axe. What would that be like?
But it's not. Instead, Demise monologues. He grunts. He looks nasty, sounds nasty, and sucks Zelda's soul up whole -- but then says, "Take your time." So I did. I went all the way back up to the Sealed Temple. Took a seat. Regenerated my hearts. Had a beer. I didn't try to go back to the future and re-arm at the Market, but it probably would have let me go back. Hell, I could have probably gone back and gathered Gratitude Crystals, while Zelda's spirit was stuck in purgatory.
Perhaps the nagging feeling some of us have, the reason why this thread/question exists, is because the momentum of the final encounter was crushed when Nintendo decided to nerf its line-up of villains by giving us time to breath. Sure, it would send beginners packing. It would undoubtedly frustrate some veterans who got "that close", but got hacked to pieces by Demise in phase 2. So what? I have spent hours getting my stats just right for a Final Fantasy final boss. And then invested more hours fighting it, only to get crushed at the bitter end. Why not push us?
I think that's the end-all issue with SS. It pushed Zelda's envelope, so-to-speak, with innovative puzzles and world design. It pushed Zelda's envelope with 1:1 motion-controlled battle. But I don't think they quite got the enemies right - but that's a different story. And the Horde-Gharihim-Demise combination may have wowed players a bit more, if it was continuous. Instead, it was segmented, and so was the tension, the stakes, and momentum, and the challenge.